U.S. patent application number 17/385554 was filed with the patent office on 2022-03-17 for eye-imaging apparatus using diffractive optical elements.
The applicant listed for this patent is Magic Leap, Inc.. Invention is credited to Evyatar Bluzer, Chunyu Gao, Michael Anthony Klug, Chulwoo Oh.
Application Number | 20220082833 17/385554 |
Document ID | / |
Family ID | 1000005988606 |
Filed Date | 2022-03-17 |
United States Patent
Application |
20220082833 |
Kind Code |
A1 |
Gao; Chunyu ; et
al. |
March 17, 2022 |
EYE-IMAGING APPARATUS USING DIFFRACTIVE OPTICAL ELEMENTS
Abstract
Examples of eye-imaging apparatus using diffractive optical
elements are provided. For example, an optical device comprises a
substrate having a proximal surface and a distal surface, a first
coupling optical element disposed on one of the proximal and distal
surfaces of the substrate, and a second coupling optical element
disposed on one of the proximal and distal surfaces of the
substrate and offset from the first coupling optical element. The
first coupling optical element can be configured to deflect light
at an angle to totally internally reflect (TIR) the light between
the proximal and distal surfaces and toward the second coupling
optical element, and the second coupling optical element can be
configured to deflect at an angle out of the substrate. The
eye-imaging apparatus can be used in a head-mounted display such as
an augmented or virtual reality display.
Inventors: |
Gao; Chunyu; (Plantation,
FL) ; Oh; Chulwoo; (Cedar Park, TX) ; Klug;
Michael Anthony; (Austin, TX) ; Bluzer; Evyatar;
(Yuvalim, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Magic Leap, Inc. |
Plantation |
FL |
US |
|
|
Family ID: |
1000005988606 |
Appl. No.: |
17/385554 |
Filed: |
July 26, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15925505 |
Mar 19, 2018 |
11073695 |
|
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17385554 |
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62474419 |
Mar 21, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 27/0179 20130101;
G02B 2027/0185 20130101; G02B 6/0076 20130101; G02B 2027/0187
20130101; G02B 2027/0178 20130101; G02B 2027/0134 20130101; G02B
27/0172 20130101; H04N 13/332 20180501; G02B 2027/0127 20130101;
G02B 27/0093 20130101; G02B 2027/0138 20130101; G06T 19/006
20130101; H04N 2213/001 20130101; G02B 2027/0123 20130101; H04N
13/383 20180501; H04N 13/344 20180501 |
International
Class: |
G02B 27/01 20060101
G02B027/01; H04N 13/383 20060101 H04N013/383; G06T 19/00 20060101
G06T019/00; H04N 13/332 20060101 H04N013/332; H04N 13/344 20060101
H04N013/344; G02B 27/00 20060101 G02B027/00 |
Claims
1. (canceled)
2. A display device comprising: an eyepiece comprising: a substrate
having a first surface and a second surface opposite the first
surface; a first coupling optical element disposed on the first
surface; and a second coupling optical element disposed on the
first surface or the second surface and laterally offset from the
first coupling optical element along a first direction parallel the
one of the first surface or the second surface on which the second
coupling optical element is disposed, wherein the first coupling
optical element is configured to deflect light at a first angle
.theta. to totally internally reflect (TIR) the light between the
first and second surfaces and toward the second coupling optical
element, the second coupling optical element configured to deflect
light at a second angle out of the substrate, and wherein the first
coupling optical element has a first width along the first
direction smaller than a stride distance of the light.
3. The optical device of claim 2, wherein the second coupling
optical element has a second width along the first direction
smaller than the stride distance.
4. The optical device of claim 2, wherein the stride distance is
proportional to tan(.theta.).
5. The optical device of claim 4, wherein the first coupling
optical element is a diffractive optical element comprising a
plurality of diffractive features, and wherein the angle .theta. is
dependent at least in part on a period or spatial frequency of the
diffractive features.
6. The optical device of claim 2, wherein the stride distance is
determined as a function of the first angle .theta. and a thickness
t of the substrate between the first surface and the second
surface.
7. The optical device of claim 6, wherein the stride distance is
equal to 2*t*tan(.theta.).
8. The optical device of claim 2, wherein the substrate is
transparent to visible light.
9. The optical device of claim 2, wherein the substrate comprises a
polymer.
10. The optical device of claim 9, wherein the polymer comprises a
polycarbonate.
11. The optical device of claim 2, wherein the first and second
coupling optical elements are external to and fixed to at least one
of the first and second surfaces of the substrate.
12. The optical device of claim 2, wherein the eyepiece comprises a
waveguide stack including a plurality of waveguides, the substrate
comprising at least a portion of one of the plurality of
waveguides.
13. The optical device of claim 2, wherein each of the first and
second coupling optical elements are configured to deflect light of
a first range of wavelengths while transmitting light of a second
range of wavelengths.
14. The optical device of claim 13, wherein the first range of
wavelengths comprises light in at least one of the infrared (IR) or
near-IR spectrum and the second range of wavelengths comprises
light in the visible spectrum.
15. A method of imaging an object using a virtual camera, the
method comprising: providing an imaging system in front of an
object to be imaged, wherein the imaging system comprises: a
substrate comprising a first coupling optical element and a second
coupling optical element, each of the first and second coupling
optical element disposed on one of a first surface and a second
surface of the substrate and offset from each other, the first
coupling optical element configured to deflect light at a first
angle to totally internally reflect (TIR) the light between the
first and second surfaces and toward the second coupling optical
element in a propagation direction, the second coupling optical
element configured to deflect the light at a second angle out of
the substrate, the first angle selected such that a stride distance
of the light is greater than a width of the first coupling optical
element along the propagation direction of the light; capturing the
light with a camera assembly oriented to receive the light
deflected by the second coupling optical element; and producing an
image of the object based on the captured light.
16. The method of claim 15, wherein the first angle is selected
such that 2*t*tan(.theta.) is greater than the width of the first
coupling optical element, where .theta. is the first angle and t is
a thickness of the substrate between the first and second
surfaces.
17. The method of claim 15, wherein the first coupling optical
element comprises a plurality of diffractive features that cause
deflection of the light, the plurality of diffractive features
having a period or spatial frequency selected to determine the
first angle.
18. The method of claim 17, wherein the eyepiece comprises a
waveguide stack including a plurality of waveguides, the substrate
comprising at least a portion of one of the plurality of
waveguides.
19. The method of claim 15, wherein each of the first and second
coupling optical elements deflect light of a first range of
wavelengths while transmitting light in a second range of
wavelengths.
20. The method of claim 15, further comprising illuminating the
object with a first range of wavelengths emitted by a light
source.
21. The method of claim 15, further comprising: analyzing the
off-axis image, and performing one or more of: eye tracking;
biometric identification; multiscopic reconstruction of a shape of
an eye; estimating an accommodation state of an eye; and imaging a
retina, iris, other distinguishing pattern of an eye, and
evaluating a physiological state of the user based, in part, on the
analyzed off-axis image.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/925,505, filed Mar. 19, 2018, entitled "EYE-IMAGING
APPARATUS USING DIFFRACTIVE OPTICAL ELEMENTS," which claims the
benefit of priority to U.S. Provisional Patent Application No.
62/474,419, filed Mar. 21, 2017, entitled "EYE-IMAGING APPARATUS
USING DIFFRACTIVE OPTICAL ELEMENTS," the contents of which are
hereby incorporated by reference herein in their entirety.
FIELD
[0002] The present disclosure relates to virtual reality and
augmented reality imaging and visualization systems and in
particular to compact imaging systems for acquiring images of an
eye using coupling optical elements to direct light to a camera
assembly.
BACKGROUND
[0003] Modern computing and display technologies have facilitated
the development of systems for so called "virtual reality" or
"augmented reality" experiences, wherein digitally reproduced
images or portions thereof are presented to a user in a manner
wherein they seem to be, or may be perceived as, real. A virtual
reality, or "VR", scenario typically involves presentation of
digital or virtual image information without transparency to other
actual real-world visual input; an augmented reality, or "AR",
scenario typically involves presentation of digital or virtual
image information as an augmentation to visualization of the actual
world around the user. A mixed reality, or "MR", scenario is a type
of AR scenario and typically involves virtual objects that are
integrated into, and responsive to, the natural world. For example,
in an MR scenario, AR image content may be blocked by or otherwise
be perceived as interacting with objects in the real world.
[0004] Referring to FIG. 1, an augmented reality scene 10 is
depicted wherein a user of an AR technology sees a real-world
park-like setting 20 featuring people, trees, buildings in the
background, and a concrete platform 30. In addition to these items,
the user of the AR technology also perceives that he "sees"
"virtual content" such as a robot statue 40 standing upon the
real-world platform 30, and a cartoon-like avatar character 50
flying by which seems to be a personification of a bumble bee, even
though these elements 40, 50 do not exist in the real world.
Because the human visual perception system is complex, it is
challenging to produce an AR technology that facilitates a
comfortable, natural-feeling, rich presentation of virtual image
elements amongst other virtual or real-world imagery elements.
[0005] Systems and methods disclosed herein address various
challenges related to AR and VR technology.
SUMMARY
[0006] Various implementations of methods and apparatus within the
scope of the appended claims each have several aspects, no single
one of which is solely responsible for the desirable attributes
described herein. Without limiting the scope of the appended
claims, some prominent features are described herein.
[0007] One aspect of the present disclosure provides imaging an
object with a camera assembly that does not directly view the
object. Accordingly, optical devices according to embodiments
described herein are configured to direct light from an object to
an off-axis camera assembly so to capture an image of the object as
if in a direct view position.
[0008] In some embodiments, systems, devices, and methods for
acquiring an image of an object using an off-axis camera assembly
are disclosed. In one implementation, an optical device is
disclosed that may include a substrate having a proximal surface
and a distal surface; a first coupling optical element disposed on
one of the proximal and distal surfaces of the substrate; and a
second coupling optical element disposed on one of the proximal and
distal surfaces of the substrate and offset from the first coupling
optical element. The first coupling optical element may be
configured to deflect light at an angle to totally internally
reflect (TIR) the light between the proximal and distal surfaces
and toward the second coupling optical element. The second coupling
optical element may be configured to deflect light at an angle out
of the substrate. In some embodiments, at least one of the first
and second coupling optical elements include a plurality of
diffractive features.
[0009] In some embodiments, systems, devices, and methods for
acquiring an image of an object using an off-axis camera assembly
are disclosed. In one implementation, a head mounted display (HMD)
configured to be worn on a head of a user is disclosed that may
include a frame; a pair of optical elements supported by the frame
such that each optical element of the pair of optical elements is
capable of being disposed forward of an eye of the user; and an
imaging system. The imaging system may include a camera assembly
mounted to the frame; and an optical device for directing light to
the camera assembly. The optical device may include a substrate
having a proximal surface and a distal surface; a first coupling
optical element disposed on one of the proximal and distal surfaces
of the substrate; and a second coupling optical element disposed on
one of the proximal and distal surfaces of the substrate and offset
from the first coupling optical element. The first coupling optical
element may be configured to deflect light at an angle to TIR the
light between the proximal and distal surfaces and toward the
second coupling optical element. The second coupling optical
element may be configured to deflect light at an angle out of the
substrate.
[0010] In some embodiments, systems, devices, and methods for
acquiring an image of an object using an off-axis camera assembly
are disclosed. In one implementation, an imaging system is
disclosed that may include a substrate having a proximal surface
and a distal surface. The substrate may include a first diffractive
optical element disposed on one of the proximal and distal surfaces
of the substrate, and a second diffractive optical element disposed
on one of the proximal and distal surfaces of the substrate and
offset from the first coupling optical element. The first
diffractive optical element may be configured to deflect light at
an angle to TIR the light between the proximal and distal surfaces
and toward the second coupling optical element. The second
diffractive optical element may be configured to deflect light
incident thereon at an angle out of the substrate. The imaging
system may also include a camera assembly to image the light
deflected by the second coupling optical element. In some
embodiments, the first and second diffractive optical elements
comprise at least one of an off-axis diffractive optical element
(DOE), an off-axis diffraction grating, an off-axis diffractive
optical element (DOE), an off-axis holographic mirror (OAHM), or an
off-axis volumetric diffractive optical element (OAVDOE), an
off-axis cholesteric liquid crystal diffraction grating (OACLCG), a
hot mirror, a prism, or a surface of a decorative lens.
[0011] In some embodiments, systems, devices, and methods for
acquiring an image of an object using an off-axis camera assembly
are disclosed. The method may include providing an imaging system
in front of an object to be imaged. The imaging system may a
substrate that may include a first coupling optical element and a
second coupling optical element each disposed on one of a proximal
surface and a distal surface of the substrate and offset from each
other. The first coupling optical element may be configured to
deflect light at an angle to TIR the light between the proximal and
distal surfaces and toward the second coupling optical element. The
second coupling optical element may be configured to deflect light
at an angle out of the substrate. The method may also include
capturing light with a camera assembly oriented to receive light
deflected by the second coupling optical element, and producing an
off-axis image of the object based on the captured light.
[0012] In any of the embodiments, the proximal surface and the
distal surface of the substrate can, but need not, be parallel to
each other. For example, the substrate may comprise a wedge.
[0013] Details of one or more implementations of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages will become apparent from the description, the drawings,
and the claims. Neither this summary nor the following detailed
description purports to define or limit the scope of the inventive
subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a user's view of augmented reality (AR)
through an AR device.
[0015] FIG. 2 illustrates an example of a wearable display
system.
[0016] FIG. 3 illustrates a conventional display system for
simulating three-dimensional imagery for a user.
[0017] FIG. 4 illustrates aspects of an approach for simulating
three-dimensional imagery using multiple depth planes.
[0018] FIGS. 5A-5C illustrate relationships between radius of
curvature and focal radius.
[0019] FIG. 6 illustrates an example of a waveguide stack for
outputting image information to a user.
[0020] FIG. 7 illustrates an example of exit beams outputted by a
waveguide.
[0021] FIG. 8 illustrates an example of a stacked waveguide
assembly in which each depth plane includes images formed using
multiple different component colors.
[0022] FIG. 9A illustrates a cross-sectional side view of an
example of a set of stacked waveguides that each includes an
in-coupling optical element.
[0023] FIG. 9B illustrates a perspective view of an example of the
plurality of stacked waveguides of FIG. 9A.
[0024] FIG. 9C illustrates a top-down plan view of an example of
the plurality of stacked waveguides of FIGS. 9A and 9B.
[0025] FIGS. 10A & 10B schematically illustrate example imaging
systems comprising a coupling optical element and a camera assembly
for tracking an eye.
[0026] FIG. 11 schematically illustrates another example imaging
system comprising multiple coupling optical elements to totally
internally reflect light from an object through a substrate to
image the object at a camera assembly.
[0027] FIG. 12A schematically illustrates another example imaging
system comprising multiple coupling optical elements to totally
internally reflect light from an object through a substrate to
image the object at a camera assembly.
[0028] FIG. 12B is an example image of the object using the imaging
system of FIG. 12A.
[0029] FIGS. 13A and 13B schematically illustrate another example
imaging system comprising multiple coupling optical elements to
totally internally reflect light from an object through a substrate
to image the object at a camera assembly.
[0030] FIGS. 14A-18 schematically illustrate several example
arrangements of imaging systems for imaging an object.
[0031] FIG. 19 is a process flow diagram of an example of a method
for imaging an object using an off-axis camera.
[0032] Throughout the drawings, reference numbers may be re-used to
indicate correspondence between referenced elements. The drawings
are provided to illustrate example embodiments described herein and
are not intended to limit the scope of the disclosure.
DETAILED DESCRIPTION
Overview
[0033] A head mounted display (HMD) might use information about the
state of the eyes of the wearer for a variety of purposes. For
example, this information can be used for estimating the gaze
direction of the wearer, for biometric identification, vision
research, evaluate a physiological state of the wearer, etc.
However, imaging the eyes can be challenging. The distance between
the HMD and the wearer's eyes is short. Furthermore, gaze tracking
requires a large field of view (FOV), while biometric
identification requires a relatively high number of pixels on
target on the iris. For imaging systems that seek to accomplish
both of these objectives, these requirements are largely at odds.
Furthermore, both problems may be further complicated by occlusion
by the eyelids and eyelashes. Some current implementations for
tracking eye movement use cameras mounted on the HMD and pointed
directly toward the eye to capture direct images of the eye.
However, in order to achieve the desired FOV and pixel number, the
cameras are mounted within the wearer's FOV, thus tend to obstruct
and interfere with the wearer's ability to see the surrounding
world. Other implementations move the camera away from obstructing
the wearer's view while directly imaging the eye, which results in
imaging the eye from a high angle causing distortions of the image
and reducing the field of view available for imaging the eye.
[0034] Embodiments of the imaging systems described herein address
some or all of these problems. Various embodiments described herein
provide apparatus and systems capable of imaging an eye while
permitting the wearer to view the surrounding world. For example,
an imaging system can comprise a substrate disposed along a line of
sight between an eye and a camera assembly. The substrate includes
one or more coupling optical elements configured to direct light
from the eye into the substrate. The substrate may act as a
light-guide (sometimes referred to as a waveguide) to direct light
toward the camera assembly. The light may then exit the substrate
and be directed to the camera assembly via one or more coupling
optical elements. The camera assembly receives the light, thus is
able to capture an image (sometimes referred to hereinafter as
"direct view image") of the eye as if in a direct view position
from a distant position (sometimes referred to herein as
"off-axis").
[0035] Some embodiments of the imaging systems described herein
provide for a substrate comprising a first and second coupling
optical element laterally offset from each other. The substrate
includes a surface that is closest to the eye (sometimes referred
to herein as the proximal surface) and a surface that is furthest
from the eye (sometimes referred to as the distal surface). The
first and second coupling optical elements described herein can be
disposed on or adjacent to the proximal surface, on or adjacent to
the distal surface, or within the substrate. The first coupling
optical element (sometimes referred to herein as an in-coupling
optical element) can be configured to deflect light from the eye
into the substrate such that the light propagates through the
substrate by total internal reflection (TIR). The light may be
incident on the second coupling optical element configured to
extract the light and deflect it toward the camera assembly. As
used herein, deflect may refer to a change in direction of light
after interacting something, for example, an optical component that
deflects light may refer to reflection, diffraction, refraction, a
change in direction while transmitting through the optical
component, etc.
[0036] In some embodiments, the imaging systems described herein
may be a portion of display optics of an HMD (or a lens in a pair
of eyeglasses). One or more coupling optical elements may be
selected to deflect on a first range of wavelengths while
permitting unhindered propagation of a second range of wavelengths
(for example, a range of wavelengths different from the first
range) through the substrate. The first range of wavelengths can be
in the infrared (IR), and the second range of wavelengths can be in
the visible. For example, the substrate can comprise a reflective
coupling optical element, which reflects IR light while
transmitting visible light. In effect, the imaging system acts as
if there were a virtual camera assembly directed back toward the
wearer's eye. Thus, virtual camera assembly can image virtual IR
light propagated from the wearer's eye through the substrate, while
visible light from the outside world can be transmitted through the
substrate and can be perceived by the wearer.
[0037] The camera assembly may be configured to view an eye of a
wearer, for example, to capture images of the eye. The camera
assembly can be mounted in proximity to the wearer's eye such that
the camera assembly does not obstruct the wearer's view of the
surrounding world or imped the operation of the HMD. In some
embodiments, the camera assembly can be positioned on a frame of a
wearable display system, for example, an ear stem or embedded in
the eyepiece of the HMD, or below the eye and over the cheek. In
some embodiments, a second camera assembly can be used for the
wearer's other eye so that each eye can be separately imaged. The
camera assembly can include an IR digital camera sensitive to IR
radiation.
[0038] The camera assembly can be mounted so that it is facing
forward (in the direction of the wearer's vision) or it can be
backward facing and directed toward the eye. In some embodiments,
by disposing the camera assembly nearer the ear of the wearer, the
weight of the camera assembly may also be nearer the ear, and the
HMD may be easier to wear as compared to an HMD where the camera
assembly is disposed nearer to the front of the HMD or in a direct
view arrangement. Additionally, by placing the camera assembly near
the wearer's temple, the distance from the wearer's eye to the
camera assembly is roughly twice as large as compared to a camera
assembly disposed near the front of the HMD. Since the depth of
field of an image is roughly proportional to this distance, the
depth of field for the camera assembly is roughly twice as large as
compared to a direct view camera assembly. A larger depth of field
for the camera assembly can be advantageous for imaging the eye
region of wearers having large or protruding noses, brow ridges,
etc. In some embodiments, the position of the camera assembly may
be based on the packaging or design considerations of the HMD. For
example, it may be advantageous to disposed the camera assembly as
a backward or forward facing in some configurations.
[0039] Without subscribing to any particular scientific theory, the
embodiments described herein may include several non-limiting
advantages. Several embodiments are capable of increasing the
physical distance between the camera assembly and the eye, which
may facilitate positioning the camera assembly out of the field of
view of the wearer's and therefore not obstructing the wearer's
view while permitting capturing of an direct view image of the eye.
Some of the embodiments described herein also may be configured to
permit eye tracking using larger field of view than conventional
systems thus allowing eye tracking over a wide range of positions.
The use of IR imaging may facilitate imaging the eye with
interfering with the wearer's ability to see through the substrate
and view the environment.
[0040] Reference will now be made to the figures, in which like
reference numerals refer to like parts throughout.
[0041] Example HMD Device
[0042] FIG. 2 illustrates an example of wearable display system 60.
The display system 60 includes a display 70, and various mechanical
and electronic modules and systems to support the functioning of
that display 70. The display 70 may be coupled to a frame 80, which
is wearable by a display system user or viewer 90 and which is
configured to position the display 70 in front of the eyes of the
user 90. The display 70 may be considered eyewear in some
embodiments. In some embodiments, a speaker 100 is coupled to the
frame 80 and configured to be positioned adjacent the ear canal of
the user 90 (in some embodiments, another speaker, not shown, is
positioned adjacent the other ear canal of the user to provide
stereo/shapeable sound control). In some embodiments, the display
system may also include one or more microphones 110 or other
devices to detect sound. In some embodiments, the microphone is
configured to allow the user to provide inputs or commands to the
system 60 (e.g., the selection of voice menu commands, natural
language questions, etc.), and/or may allow audio communication
with other persons (e.g., with other users of similar display
systems. The microphone may further be configured as a peripheral
sensor to collect audio data (e.g., sounds from the user and/or
environment). In some embodiments, the display system may also
include a peripheral sensor 120a, which may be separate from the
frame 80 and attached to the body of the user 90 (e.g., on the
head, torso, an extremity, etc. of the user 90). The peripheral
sensor 120a may be configured to acquire data characterizing the
physiological state of the user 90 in some embodiments. For
example, the sensor 120a may be an electrode.
[0043] With continued reference to FIG. 2, the display 70 is
operatively coupled by communications link 130, such as by a wired
lead or wireless connectivity, to a local data processing module
140 which may be mounted in a variety of configurations, such as
fixedly attached to the frame 80, fixedly attached to a helmet or
hat worn by the user, embedded in headphones, or otherwise
removably attached to the user 90 (e.g., in a backpack-style
configuration, in a belt-coupling style configuration). Similarly,
the sensor 120a may be operatively coupled by communications link
120b, e.g., a wired lead or wireless connectivity, to the local
processor and data module 140. The local processing and data module
140 may comprise a hardware processor, as well as digital memory,
such as non-volatile memory (e.g., flash memory or hard disk
drives), both of which may be utilized to assist in the processing,
caching, and storage of data. The data may include data a) captured
from sensors (which may be, e.g., operatively coupled to the frame
80 or otherwise attached to the user 90), such as image capture
devices (such as, for example, cameras), microphones, inertial
measurement units, accelerometers, compasses, GPS units, radio
devices, gyros, and/or other sensors disclosed herein; and/or b)
acquired and/or processed using remote processing module 150 and/or
remote data repository 160 (including data relating to virtual
content), possibly for passage to the display 70 after such
processing or retrieval. The local processing and data module 140
may be operatively coupled by communication links 170, 180, such as
via a wired or wireless communication links, to the remote
processing module 150 and remote data repository 160 such that
these remote modules 150, 160 are operatively coupled to each other
and available as resources to the local processing and data module
140. In some embodiments, the local processing and data module 140
may include one or more of the image capture devices, microphones,
inertial measurement units, accelerometers, compasses, GPS units,
radio devices, and/or gyros. In some other embodiments, one or more
of these sensors may be attached to the frame 80, or may be
standalone structures that communicate with the local processing
and data module 140 by wired or wireless communication
pathways.
[0044] With continued reference to FIG. 2, in some embodiments, the
remote processing module 150 may comprise one or more processors
configured to analyze and process data and/or image information. In
some embodiments, the remote data repository 160 may comprise a
digital data storage facility, which may be available through the
internet or other networking configuration in a "cloud" resource
configuration. In some embodiments, the remote data repository 160
may include one or more remote servers, which provide information,
e.g., information for generating augmented reality content, to the
local processing and data module 140 and/or the remote processing
module 150. In some embodiments, all data is stored and all
computations are performed in the local processing and data module,
allowing fully autonomous use from a remote module.
[0045] The perception of an image as being "three-dimensional" or
"3-D" may be achieved by providing slightly different presentations
of the image to each eye of the viewer. FIG. 3 illustrates a
conventional display system for simulating three-dimensional
imagery for a user. Two distinct images 190, 200--one for each eye
210, 220--are outputted to the user. The images 190, 200 are spaced
from the eyes 210, 220 by a distance 230 along an optical or z-axis
that is parallel to the line of sight of the viewer. The images
190, 200 are flat and the eyes 210, 220 may focus on the images by
assuming a single accommodated state. Such 3-D display systems rely
on the human visual system to combine the images 190, 200 to
provide a perception of depth and/or scale for the combined
image.
[0046] It will be appreciated, however, that the human visual
system is more complicated and providing a realistic perception of
depth is more challenging. For example, many viewers of
conventional "3-D" display systems find such systems to be
uncomfortable or may not perceive a sense of depth at all. Without
being limited by theory, it is believed that viewers of an object
may perceive the object as being "three-dimensional" due to a
combination of vergence and accommodation. Vergence movements
(e.g., rotation of the eyes so that the pupils move toward or away
from each other to converge the lines of sight of the eyes to
fixate upon an object) of the two eyes relative to each other are
closely associated with focusing (or "accommodation") of the lenses
and pupils of the eyes. Under normal conditions, changing the focus
of the lenses of the eyes, or accommodating the eyes, to change
focus from one object to another object at a different distance
will automatically cause a matching change in vergence to the same
distance, under a relationship known as the "accommodation-vergence
reflex," as well as pupil dilation or constriction. Likewise, a
change in vergence will trigger a matching change in accommodation
of lens shape and pupil size, under normal conditions. As noted
herein, many stereoscopic or "3-D" display systems display a scene
using slightly different presentations (and, so, slightly different
images) to each eye such that a three-dimensional perspective is
perceived by the human visual system. Such systems are
uncomfortable for many viewers, however, since they, among other
things, simply provide a different presentation of a scene, but
with the eyes viewing all the image information at a single
accommodated state, and work against the "accommodation-vergence
reflex." Display systems that provide a better match between
accommodation and vergence may form more realistic and comfortable
simulations of three-dimensional imagery contributing to increased
duration of wear and in turn compliance to diagnostic and therapy
protocols.
[0047] FIG. 4 illustrates aspects of an approach for simulating
three-dimensional imagery using multiple depth planes. With
reference to FIG. 4, objects at various distances from eyes 210,
220 on the z-axis are accommodated by the eyes 210, 220 so that
those objects are in focus. The eyes 210, 220 assume particular
accommodated states to bring into focus objects at different
distances along the z-axis. Consequently, a particular accommodated
state may be said to be associated with a particular one of depth
planes 240, which has an associated focal distance, such that
objects or parts of objects in a particular depth plane are in
focus when the eye is in the accommodated state for that depth
plane. In some embodiments, three-dimensional imagery may be
simulated by providing different presentations of an image for each
of the eyes 210, 220, and also by providing different presentations
of the image corresponding to each of the depth planes. While shown
as being separate for clarity of illustration, it will be
appreciated that the fields of view of the eyes 210, 220 may
overlap, for example, as distance along the z-axis increases. In
addition, while shown as flat for ease of illustration, it will be
appreciated that the contours of a depth plane may be curved in
physical space, such that all features in a depth plane are in
focus with the eye in a particular accommodated state.
[0048] The distance between an object and the eye 210 or 220 may
also change the amount of divergence of light from that object, as
viewed by that eye. FIGS. 5A-5C illustrate relationships between
distance and the divergence of light rays. The distance between the
object and the eye 210 is represented by, in order of decreasing
distance, R1, R2, and R3. As shown in FIGS. 5A-5C, the light rays
become more divergent as distance to the object decreases. As
distance increases, the light rays become more collimated. Stated
another way, it may be said that the light field produced by a
point (the object or a part of the object) has a spherical
wavefront curvature, which is a function of how far away the point
is from the eye of the user. The curvature increases with
decreasing distance between the object and the eye 210.
Consequently, at different depth planes, the degree of divergence
of light rays is also different, with the degree of divergence
increasing with decreasing distance between depth planes and the
viewer's eye 210. While only a single eye 210 is illustrated for
clarity of illustration in FIGS. 5A-5C and other figures herein, it
will be appreciated that the discussions regarding eye 210 may be
applied to both eyes 210 and 220 of a viewer.
[0049] Without being limited by theory, it is believed that the
human eye typically can interpret a finite number of depth planes
to provide depth perception. Consequently, a highly believable
simulation of perceived depth may be achieved by providing, to the
eye, different presentations of an image corresponding to each of
these limited number of depth planes. The different presentations
may be separately focused by the viewer's eyes, thereby helping to
provide the user with depth cues based on the accommodation of the
eye required to bring into focus different image features for the
scene located on different depth plane and/or based on observing
different image features on different depth planes being out of
focus.
[0050] Example of a Waveguide Stack Assembly
[0051] FIG. 6 illustrates an example of a waveguide stack for
outputting image information to a user. A display system 250
includes a stack of waveguides, or stacked waveguide assembly, 260
that may be utilized to provide three-dimensional perception to the
eye/brain using a plurality of waveguides 270, 280, 290, 300, 310.
In some embodiments, the display system 250 is the system 60 of
FIG. 2, with FIG. 6 schematically showing some parts of that system
60 in greater detail. For example, the waveguide assembly 260 may
be part of the display 70 of FIG. 2. It will be appreciated that
the display system 250 may be considered a light field display in
some embodiments.
[0052] With continued reference to FIG. 6, the waveguide assembly
260 may also include a plurality of features 320, 330, 340, 350
between the waveguides. In some embodiments, the features 320, 330,
340, 350 may be one or more lenses. The waveguides 270, 280, 290,
300, 310 and/or the plurality of lenses 320, 330, 340, 350 may be
configured to send image information to the eye with various levels
of wavefront curvature or light ray divergence. Each waveguide
level may be associated with a particular depth plane and may be
configured to output image information corresponding to that depth
plane. Image injection devices 360, 370, 380, 390, 400 may function
as a source of light for the waveguides and may be utilized to
inject image information into the waveguides 270, 280, 290, 300,
310, each of which may be configured, as described herein, to
distribute incoming light across each respective waveguide, for
output toward the eye 210. Light exits an output surface 410, 420,
430, 440, 450 of the image injection devices 360, 370, 380, 390,
400 and is injected into a corresponding input surface 460, 470,
480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some
embodiments, the each of the input surfaces 460, 470, 480, 490, 500
may be an edge of a corresponding waveguide, or may be part of a
major surface of the corresponding waveguide (that is, one of the
waveguide surfaces directly facing the world 510 or the viewer's
eye 210). In some embodiments, a single beam of light (e.g. a
collimated beam) may be injected into each waveguide to output an
entire field of cloned collimated beams that are directed toward
the eye 210 at particular angles (and amounts of divergence)
corresponding to the depth plane associated with a particular
waveguide. In some embodiments, a single one of the image injection
devices 360, 370, 380, 390, 400 may be associated with and inject
light into a plurality (e.g., three) of the waveguides 270, 280,
290, 300, 310.
[0053] In some embodiments, the image injection devices 360, 370,
380, 390, 400 are discrete displays that each produce image
information for injection into a corresponding waveguide 270, 280,
290, 300, 310, respectively. In some other embodiments, the image
injection devices 360, 370, 380, 390, 400 are the output ends of a
single multiplexed display which may, e.g., pipe image information
via one or more optical conduits (such as fiber optic cables) to
each of the image injection devices 360, 370, 380, 390, 400. It
will be appreciated that the image information provided by the
image injection devices 360, 370, 380, 390, 400 may include light
of different wavelengths, or colors (e.g., different component
colors, as discussed herein).
[0054] In some embodiments, the light injected into the waveguides
270, 280, 290, 300, 310 is provided by a light projector system
520, which comprises a light module 530, which may include a light
emitter, such as a light emitting diode (LED). The light from the
light module 530 may be directed to and modified by a light
modulator 540, e.g., a spatial light modulator, via a beam splitter
550. The light modulator 540 may be configured to change the
perceived intensity of the light injected into the waveguides 270,
280, 290, 300, 310. Examples of spatial light modulators include
liquid crystal displays (LCD) including a liquid crystal on silicon
(LCOS) displays.
[0055] In some embodiments, the display system 250 may be a
scanning fiber display comprising one or more scanning fibers
configured to project light in various patterns (e.g., raster scan,
spiral scan, Lissajous patterns, etc.) into one or more waveguides
270, 280, 290, 300, 310 and ultimately to the eye 210 of the
viewer. In some embodiments, the illustrated image injection
devices 360, 370, 380, 390, 400 may schematically represent a
single scanning fiber or a bundle of scanning fibers configured to
inject light into one or a plurality of the waveguides 270, 280,
290, 300, 310. In some other embodiments, the illustrated image
injection devices 360, 370, 380, 390, 400 may schematically
represent a plurality of scanning fibers or a plurality of bundles
of scanning fibers, each of which are configured to inject light
into an associated one of the waveguides 270, 280, 290, 300, 310.
It will be appreciated that one or more optical fibers may be
configured to transmit light from the light module 530 to the one
or more waveguides 270, 280, 290, 300, and 310. It will be
appreciated that one or more intervening optical structures may be
provided between the scanning fiber, or fibers, and the one or more
waveguides 270, 280, 290, 300, 310 to, e.g., redirect light exiting
the scanning fiber into the one or more waveguides 270, 280, 290,
300, 310.
[0056] A controller 560 controls the operation of one or more of
the stacked waveguide assembly 260, including operation of the
image injection devices 360, 370, 380, 390, 400, the light source
530, and the light modulator 540. In some embodiments, the
controller 560 is part of the local data processing module 140. The
controller 560 includes programming (e.g., instructions in a
non-transitory medium) that regulates the timing and provision of
image information to the waveguides 270, 280, 290, 300, 310
according to, e.g., any of the various schemes disclosed herein. In
some embodiments, the controller may be a single integral device,
or a distributed system connected by wired or wireless
communication channels. The controller 560 may be part of the
processing modules 140 or 150 (FIG. 2) in some embodiments.
[0057] With continued reference to FIG. 6, the waveguides 270, 280,
290, 300, 310 may be configured to propagate light within each
respective waveguide by TIR. The waveguides 270, 280, 290, 300, 310
may each be planar or have another shape (e.g., curved), with major
top and bottom surfaces and edges extending between those major top
and bottom surfaces. In the illustrated configuration, the
waveguides 270, 280, 290, 300, 310 may each include out-coupling
optical elements 570, 580, 590, 600, 610 that are configured to
extract light out of a waveguide by redirecting the light,
propagating within each respective waveguide, out of the waveguide
to output image information to the eye 210. Extracted light may
also be referred to as out-coupled light and the out-coupling
optical elements light may also be referred to light extracting
optical elements. An extracted beam of light may be outputted by
the waveguide at locations at which the light propagating in the
waveguide strikes a light extracting optical element. The
out-coupling optical elements 570, 580, 590, 600, 610 may, for
example, be gratings, including diffractive optical features, as
discussed further herein. While illustrated disposed at the bottom
major surfaces of the waveguides 270, 280, 290, 300, 310, for ease
of description and drawing clarity, in some embodiments, the
out-coupling optical elements 570, 580, 590, 600, 610 may be
disposed at the top and/or bottom major surfaces, and/or may be
disposed directly in the volume of the waveguides 270, 280, 290,
300, 310, as discussed further herein. In some embodiments, the
out-coupling optical elements 570, 580, 590, 600, 610 may be formed
in a layer of material that is attached to a transparent substrate
to form the waveguides 270, 280, 290, 300, 310. In some other
embodiments, the waveguides 270, 280, 290, 300, 310 may be a
monolithic piece of material and the out-coupling optical elements
570, 580, 590, 600, 610 may be formed on a surface and/or in the
interior of that piece of material.
[0058] With continued reference to FIG. 6, as discussed herein,
each waveguide 270, 280, 290, 300, 310 is configured to output
light to form an image corresponding to a particular depth plane.
For example, the waveguide 270 nearest the eye may be configured to
deliver collimated light (which was injected into such waveguide
270), to the eye 210. The collimated light may be representative of
the optical infinity focal plane. The next waveguide up 280 may be
configured to send out collimated light which passes through the
first lens 350 (e.g., a negative lens) before it can reach the eye
210; such first lens 350 may be configured to create a slight
convex wavefront curvature so that the eye/brain interprets light
coming from that next waveguide up 280 as coming from a first focal
plane closer inward toward the eye 210 from optical infinity.
Similarly, the third up waveguide 290 passes its output light
through both the first 350 and second 340 lenses before reaching
the eye 210; the combined optical power of the first 350 and second
340 lenses may be configured to create another incremental amount
of wavefront curvature so that the eye/brain interprets light
coming from the third waveguide 290 as coming from a second focal
plane that is even closer inward toward the person from optical
infinity than was light from the next waveguide up 280.
[0059] The other waveguide layers 300, 310 and lenses 330, 320 are
similarly configured, with the highest waveguide 310 in the stack
sending its output through all of the lenses between it and the eye
for an aggregate focal power representative of the closest focal
plane to the person. To compensate for the stack of lenses 320,
330, 340, 350 when viewing/interpreting light coming from the world
510 on the other side of the stacked waveguide assembly 260, a
compensating lens layer 620 may be disposed at the top of the stack
to compensate for the aggregate power of the lens stack 320, 330,
340, 350 below. Such a configuration provides as many perceived
focal planes as there are available waveguide/lens pairings. Both
the out-coupling optical elements of the waveguides and the
focusing aspects of the lenses may be static (i.e., not dynamic or
electro-active). In some alternative embodiments, either or both
may be dynamic using electro-active features.
[0060] In some embodiments, two or more of the waveguides 270, 280,
290, 300, 310 may have the same associated depth plane. For
example, multiple waveguides 270, 280, 290, 300, 310 may be
configured to output images set to the same depth plane, or
multiple subsets of the waveguides 270, 280, 290, 300, 310 may be
configured to output images set to the same plurality of depth
planes, with one set for each depth plane. This can provide
advantages for forming a tiled image to provide an expanded field
of view at those depth planes.
[0061] With continued reference to FIG. 6, the out-coupling optical
elements 570, 580, 590, 600, 610 may be configured to both redirect
light out of their respective waveguides and to output this light
with the appropriate amount of divergence or collimation for a
particular depth plane associated with the waveguide. As a result,
waveguides having different associated depth planes may have
different configurations of out-coupling optical elements 570, 580,
590, 600, 610, which output light with a different amount of
divergence depending on the associated depth plane. In some
embodiments, the light extracting optical elements 570, 580, 590,
600, 610 may be volumetric or surface features, which may be
configured to output light at specific angles. For example, the
light extracting optical elements 570, 580, 590, 600, 610 may be
volume holograms, surface holograms, and/or diffraction gratings.
In some embodiments, the features 320, 330, 340, 350 may not be
lenses; rather, they may simply be spacers (e.g., cladding layers
and/or structures for forming air gaps).
[0062] In some embodiments, the out-coupling optical elements 570,
580, 590, 600, 610 are diffractive features that form a diffraction
pattern, or "diffractive optical element" (also referred to herein
as a "DOE"). Preferably, the DOE's have a sufficiently low
diffraction efficiency so that only a portion of the light of the
beam is deflected away toward the eye 210 with each intersection of
the DOE, while the rest continues to move through a waveguide via
TIR. The light carrying the image information is thus divided into
a number of related exit beams that exit the waveguide at a
multiplicity of locations and the result is a fairly uniform
pattern of exit emission toward the eye 210 for this particular
collimated beam bouncing around within a waveguide.
[0063] In some embodiments, one or more DOEs may be switchable
between "on" states in which they actively diffract, and "off"
states in which they do not significantly diffract. For instance, a
switchable DOE may comprise a layer of polymer dispersed liquid
crystal, in which microdroplets comprise a diffraction pattern in a
host medium, and the refractive index of the microdroplets may be
switched to substantially match the refractive index of the host
material (in which case the pattern does not appreciably diffract
incident light) or the microdroplet may be switched to an index
that does not match that of the host medium (in which case the
pattern actively diffracts incident light).
[0064] In some embodiments, a camera assembly 630 (e.g., a digital
camera, including visible light and IR light cameras) may be
provided to capture images of the eye 210, parts of the eye 210, or
at least a portion of the tissue surrounding the eye 210 to, e.g.,
detect user inputs, extract biometric information from the eye,
estimate and track the gaze of the direction of the eye, to monitor
the physiological state of the user, etc. As used herein, a camera
may be any image capture device. In some embodiments, the camera
assembly 630 may include an image capture device and a light source
632 to project light (e.g., IR or near-IR light) to the eye, which
may then be reflected by the eye and detected by the image capture
device. In some embodiments, the light source 632 includes light
emitting diodes ("LEDs"), emitting in IR or near-IR. While the
light source 632 is illustrated as attached to the camera assembly
630, it will be appreciated that the light source 632 may be
disposed in other areas with respect to the camera assembly such
that light emitted by the light source is directed to the eye of
the wearer (e.g., light source 530 described below). In some
embodiments, the camera assembly 630 may be attached to the frame
80 (FIG. 2) and may be in electrical communication with the
processing modules 140 or 150, which may process image information
from the camera assembly 630 to make various determinations
regarding, e.g., the physiological state of the user, the gaze
direction of the wearer, iris identification, etc., as discussed
herein. It will be appreciated that information regarding the
physiological state of user may be used to determine the behavioral
or emotional state of the user. Examples of such information
include movements of the user or facial expressions of the user.
The behavioral or emotional state of the user may then be
triangulated with collected environmental or virtual content data
so as to determine relationships between the behavioral or
emotional state, physiological state, and environmental or virtual
content data. In some embodiments, one camera assembly 630 may be
utilized for each eye, to separately monitor each eye.
[0065] With reference now to FIG. 7, an example of exit beams
outputted by a waveguide is shown. One waveguide is illustrated,
but it will be appreciated that other waveguides in the waveguide
assembly 260 (FIG. 6) may function similarly, where the waveguide
assembly 260 includes multiple waveguides. Light 640 is injected
into the waveguide 270 at the input surface 460 of the waveguide
270 and propagates within the waveguide 270 by TIR. At points where
the light 640 impinges on the DOE 570, a portion of the light exits
the waveguide as exit beams 650. The exit beams 650 are illustrated
as substantially parallel but, as discussed herein, they may also
be redirected to propagate to the eye 210 at an angle (e.g.,
forming divergent exit beams), depending on the depth plane
associated with the waveguide 270. Substantially parallel exit
beams may be indicative of a waveguide with out-coupling optical
elements that out-couple light to form images that appear to be set
on a depth plane at a large distance (e.g., optical infinity) from
the eye 210. Other waveguides or other sets of out-coupling optical
elements may output an exit beam pattern that is more divergent,
which would require the eye 210 to accommodate to a closer distance
to bring it into focus on the retina and would be interpreted by
the brain as light from a distance closer to the eye 210 than
optical infinity.
[0066] In some embodiments, a full color image may be formed at
each depth plane by overlaying images in each of the component
colors, e.g., three or more component colors. FIG. 8 illustrates an
example of a stacked waveguide assembly in which each depth plane
includes images formed using multiple different component colors.
The illustrated embodiment shows depth planes 240a-240f, although
more or fewer depths are also contemplated. Each depth plane may
have three or more component color images associated with it,
including: a first image of a first color, G; a second image of a
second color, R; and a third image of a third color, B. Different
depth planes are indicated in the figure by different numbers for
diopters (dpt) following the letters G, R, and B. Just as examples,
the numbers following each of these letters indicate diopters
(l/m), or inverse distance of the depth plane from a viewer, and
each box in the figures represents an individual component color
image. In some embodiments, to account for differences in the eye's
focusing of light of different wavelengths, the exact placement of
the depth planes for different component colors may vary. For
example, different component color images for a given depth plane
may be placed on depth planes corresponding to different distances
from the user. Such an arrangement may increase visual acuity and
user comfort or may decrease chromatic aberrations.
[0067] In some embodiments, light of each component color may be
outputted by a single dedicated waveguide and, consequently, each
depth plane may have multiple waveguides associated with it. In
such embodiments, each box in the figures including the letters G,
R, or B may be understood to represent an individual waveguide, and
three waveguides may be provided per depth plane where three
component color images are provided per depth plane. While the
waveguides associated with each depth plane are shown adjacent to
one another in this drawing for ease of description, it will be
appreciated that, in a physical device, the waveguides may all be
arranged in a stack with one waveguide per level. In some other
embodiments, multiple component colors may be outputted by the same
waveguide, such that, e.g., only a single waveguide may be provided
per depth plane.
[0068] With continued reference to FIG. 8, in some embodiments, G
is the color green, R is the color red, and B is the color blue. In
some other embodiments, other colors associated with other
wavelengths of light, including magenta and cyan, may be used in
addition to or may replace one or more of red, green, or blue. In
some embodiments, features 320, 330, 340, and 350 may be active or
passive optical filters configured to block or selectively pass
light from the ambient environment to the viewer's eyes.
[0069] It will be appreciated that references to a given color of
light throughout this disclosure will be understood to encompass
light of one or more wavelengths within a range of wavelengths of
light that are perceived by a viewer as being of that given color.
For example, red light may include light of one or more wavelengths
in the range of about 620-780 nm, green light may include light of
one or more wavelengths in the range of about 492-577 nm, and blue
light may include light of one or more wavelengths in the range of
about 435-493 nm.
[0070] In some embodiments, the light source 530 (FIG. 6) may be
configured to emit light of one or more wavelengths outside the
visual perception range of the viewer, for example, IR or
ultraviolet wavelengths. IR light can include light with
wavelengths in a range from 700 nm to 10 .mu.m. In some
embodiments, IR light can include near-IR light with wavelengths in
a range from 700 nm to 1.5 .mu.m. In addition, the in-coupling,
out-coupling, and other light redirecting structures of the
waveguides of the display 250 may be configured to direct and emit
this light out of the display towards the user's eye 210, e.g., for
imaging or user stimulation applications.
[0071] With reference now to FIG. 9A, in some embodiments, light
impinging on a waveguide may need to be redirected to in-couple the
light into the waveguide. An in-coupling optical element may be
used to redirect and in-couple the light into its corresponding
waveguide. FIG. 9A illustrates a cross-sectional side view of an
example of a plurality or set 660 of stacked waveguides that each
includes an in-coupling optical element. The waveguides may each be
configured to output light of one or more different wavelengths, or
one or more different ranges of wavelengths. It will be appreciated
that the stack 660 may correspond to the stack 260 (FIG. 6) and the
illustrated waveguides of the stack 660 may correspond to part of
the plurality of waveguides 270, 280, 290, 300, 310, except that
light from one or more of the image injection devices 360, 370,
380, 390, 400 is injected into the waveguides from a position that
requires light to be redirected for in-coupling.
[0072] The illustrated set 660 of stacked waveguides includes
waveguides 670, 680, and 690. Each waveguide includes an associated
in-coupling optical element (which may also be referred to as a
light input area on the waveguide), with, e.g., in-coupling optical
element 700 disposed on a major surface (e.g., an upper major
surface) of waveguide 670, in-coupling optical element 710 disposed
on a major surface (e.g., an upper major surface) of waveguide 680,
and in-coupling optical element 720 disposed on a major surface
(e.g., an upper major surface) of waveguide 690. In some
embodiments, one or more of the in-coupling optical elements 700,
710, 720 may be disposed on the bottom major surface of the
respective waveguide 670, 680, 690 (particularly where the one or
more in-coupling optical elements are reflective, deflecting
optical elements). As illustrated, the in-coupling optical elements
700, 710, 720 may be disposed on the upper major surface of their
respective waveguide 670, 680, 690 (or the top of the next lower
waveguide), particularly where those in-coupling optical elements
are transmissive, deflecting optical elements. In some embodiments,
the in-coupling optical elements 700, 710, 720 may be disposed in
the body of the respective waveguide 670, 680, 690. In some
embodiments, as discussed herein, the in-coupling optical elements
700, 710, 720 are wavelength selective, such that they selectively
redirect one or more wavelengths of light, while transmitting other
wavelengths of light. While illustrated on one side or corner of
their respective waveguide 670, 680, 690, it will be appreciated
that the in-coupling optical elements 700, 710, 720 may be disposed
in other areas of their respective waveguide 670, 680, 690 in some
embodiments.
[0073] As illustrated, the in-coupling optical elements 700, 710,
720 may be laterally offset from one another. In some embodiments,
each in-coupling optical element may be offset such that it
receives light without that light passing through another
in-coupling optical element. For example, each in-coupling optical
element 700, 710, 720 may be configured to receive light from a
different image injection device 360, 370, 380, 390, and 400 as
shown in FIG. 6, and may be separated (e.g., laterally spaced
apart) from other in-coupling optical elements 700, 710, 720 such
that it substantially does not receive light from the other ones of
the in-coupling optical elements 700, 710, 720.
[0074] Each waveguide also includes associated light distributing
elements, with, e.g., light distributing elements 730 disposed on a
major surface (e.g., a top major surface) of waveguide 670, light
distributing elements 740 disposed on a major surface (e.g., a top
major surface) of waveguide 680, and light distributing elements
750 disposed on a major surface (e.g., a top major surface) of
waveguide 690. In some other embodiments, the light distributing
elements 730, 740, 750 may be disposed on a bottom major surface of
associated waveguides 670, 680, 690, respectively. In some other
embodiments, the light distributing elements 730, 740, 750 may be
disposed on both top and bottom major surface of associated
waveguides 670, 680, 690 respectively; or the light distributing
elements 730, 740, 750, may be disposed on different ones of the
top and bottom major surfaces in different associated waveguides
670, 680, 690, respectively.
[0075] The waveguides 670, 680, 690 may be spaced apart and
separated by, e.g., gas, liquid, or solid layers of material. For
example, as illustrated, layer 760a may separate waveguides 670 and
680; and layer 760b may separate waveguides 680 and 690. In some
embodiments, the layers 760a and 760b are formed of low refractive
index materials (that is, materials having a lower refractive index
than the material forming the immediately adjacent one of
waveguides 670, 680, 690). Preferably, the refractive index of the
material forming the layers 760a, 760b is 0.05 or more, or 0.10 or
less than the refractive index of the material forming the
waveguides 670, 680, 690. Advantageously, the lower refractive
index layers 760a, 760b may function as cladding layers that
facilitate TIR of light through the waveguides 670, 680, 690 (e.g.,
TIR between the top and bottom major surfaces of each waveguide).
In some embodiments, the layers 760a, 760b are formed of air. While
not illustrated, it will be appreciated that the top and bottom of
the illustrated set 660 of waveguides may include immediately
neighboring cladding layers.
[0076] Preferably, for ease of manufacturing and other
considerations, the material forming the waveguides 670, 680, 690
are similar or the same, and the material forming the layers 760a,
760b are similar or the same. In some embodiments, the material
forming the waveguides 670, 680, 690 may be different between one
or more waveguides, or the material forming the layers 760a, 760b
may be different, while still holding to the various refractive
index relationships noted above.
[0077] With continued reference to FIG. 9A, light rays 770, 780,
790 are incident on the set 660 of waveguides. It will be
appreciated that the light rays 770, 780, 790 may be injected into
the waveguides 670, 680, 690 by one or more image injection devices
360, 370, 380, 390, 400 (FIG. 6).
[0078] In some embodiments, the light rays 770, 780, 790 have
different properties, e.g., different wavelengths or different
ranges of wavelengths, which may correspond to different colors.
The in-coupling optical elements 700, 710, 720 each deflect the
incident light such that the light propagates through a respective
one of the waveguides 670, 680, 690 by TIR.
[0079] For example, in-coupling optical element 700 may be
configured to deflect ray 770, which has a first wavelength or
range of wavelengths. Similarly, the transmitted ray 780 impinges
on and is deflected by the in-coupling optical element 710, which
is configured to deflect light of a second wavelength or range of
wavelengths. Likewise, the ray 790 is deflected by the in-coupling
optical element 720, which is configured to selectively deflect
light of third wavelength or range of wavelengths.
[0080] With continued reference to FIG. 9A, the deflected light
rays 770, 780, 790 are deflected so that they propagate through a
corresponding waveguide 670, 680, 690; that is, the in-coupling
optical elements 700, 710, 720 of each waveguide deflects light
into that corresponding waveguide 670, 680, 690 to in-couple light
into that corresponding waveguide. The light rays 770, 780, 790 are
deflected at angles that cause the light to propagate through the
respective waveguide 670, 680, 690 by TIR. The light rays 770, 780,
790 propagate through the respective waveguide 670, 680, 690 by TIR
until impinging on the waveguide's corresponding light distributing
elements 730, 740, 750.
[0081] With reference now to FIG. 9B, a perspective view of an
example of the plurality of stacked waveguides of FIG. 9A is
illustrated. As noted above, the in-coupled light rays 770, 780,
790, are deflected by the in-coupling optical elements 700, 710,
720, respectively, and then propagate by TIR within the waveguides
670, 680, 690, respectively. The light rays 770, 780, 790 then
impinge on the light distributing elements 730, 740, 750,
respectively. The light distributing elements 730, 740, 750 deflect
the light rays 770, 780, 790 so that they propagate towards the
out-coupling optical elements 800, 810, and 820, respectively.
[0082] In some embodiments, the light distributing elements 730,
740, 750 are orthogonal pupil expanders (OPE's). In some
embodiments, the OPE's both deflect or distribute light to the
out-coupling optical elements 800, 810, 820 and also increase the
beam or spot size of this light as it propagates to the
out-coupling optical elements. In some embodiments, e.g., where the
beam size is already of a desired size, the light distributing
elements 730, 740, 750 may be omitted and the in-coupling optical
elements 700, 710, 720 may be configured to deflect light directly
to the out-coupling optical elements 800, 810, 820. For example,
with reference to FIG. 9A, the light distributing elements 730,
740, 750 may be replaced with out-coupling optical elements 800,
810, 820, respectively. In some embodiments, the out-coupling
optical elements 800, 810, 820 are exit pupils (EP's) or exit pupil
expanders (EPE's) that direct light in a viewer's eye 210 (FIG. 7).
It will be appreciated that the OPE's may be configured to increase
the dimensions of the eye box in at least one axis and the EPE's
may be to increase the eye box in an axis crossing, e.g.,
orthogonal to, the axis of the OPEs.
[0083] Accordingly, with reference to FIGS. 9A and 9B, in some
embodiments, the set 660 of waveguides includes waveguides 670,
680, 690; in-coupling optical elements 700, 710, 720; light
distributing elements (e.g., OPE's) 730, 740, 750; and out-coupling
optical elements (e.g., EP's) 800, 810, 820 for each component
color. The waveguides 670, 680, 690 may be stacked with an air
gap/cladding layer between each one. The in-coupling optical
elements 700, 710, 720 redirect or deflect incident light (with
different in-coupling optical elements receiving light of different
wavelengths) into its waveguide. The light then propagates at an
angle that will result in TIR within the respective waveguide 670,
680, 690. In the example shown, light ray 770 (e.g., blue light) is
deflected by the first in-coupling optical element 700, and then
continues to bounce down the waveguide, interacting with the light
distributing element (e.g., OPE's) 730 and then the out-coupling
optical element (e.g., EPs) 800, in a manner described earlier. The
light rays 780 and 790 (e.g., green and red light, respectively)
will pass through the waveguide 670, with light ray 780 impinging
on and being deflected by in-coupling optical element 710. The
light ray 780 then bounces down the waveguide 680 via TIR,
proceeding on to its light distributing element (e.g., OPEs) 740
and then the out-coupling optical element (e.g., EP's) 810.
Finally, light ray 790 (e.g., red light) passes through the
waveguide 690 to impinge on the light in-coupling optical elements
720 of the waveguide 690. The light in-coupling optical elements
720 deflect the light ray 790 such that the light ray propagates to
light distributing element (e.g., OPEs) 750 by TIR, and then to the
out-coupling optical element (e.g., EPs) 820 by TIR. The
out-coupling optical element 820 then finally out-couples the light
ray 790 to the viewer, who also receives the out-coupled light from
the other waveguides 670, 680.
[0084] FIG. 9C illustrates a top-down plan view of an example of
the plurality of stacked waveguides of FIGS. 9A and 9B. As
illustrated, the waveguides 670, 680, 690, along with each
waveguide's associated light distributing element 730, 740, 750 and
associated out-coupling optical element 800, 810, 820, may be
vertically aligned. However, as discussed herein, the in-coupling
optical elements 700, 710, 720 are not vertically aligned; rather,
the in-coupling optical elements are preferably non-overlapping
(e.g., laterally spaced apart as seen in the top-down view). As
discussed further herein, this non-overlapping spatial arrangement
facilitates the injection of light from different resources into
different waveguides on a one-to-one basis, thereby allowing a
specific light source to be uniquely coupled to a specific
waveguide. In some embodiments, arrangements including
non-overlapping spatially separated in-coupling optical elements
may be referred to as a shifted pupil system, and the in-coupling
optical elements within these arrangements may correspond to sub
pupils.
[0085] Example Imaging Systems for Off-Axis Imaging
[0086] As described above, the eyes or tissue around the eyes of
the wearer of a HMD (e.g., the wearable display system 200 shown in
FIG. 2) can be imaged using multiple coupling optical elements to
direct light from the eye through a substrate and into a camera
assembly. The resulting images can be used to track an eye or eyes,
image the retina, reconstruct the eye shape in three dimensions,
extract biometric information from the eye (e.g., iris
identification), etc.
[0087] As outlined above, there are a variety of reasons why a HMD
might use information about the state of the eyes of the wearer.
For example, this information can be used for estimating the gaze
direction of the wearer or for biometric identification. This
problem is challenging, however, because of the short distance
between the HMD and the wearer's eyes. It is further complicated by
the fact that gaze tracking requires a larger field of view, while
biometric identification requires a relatively high number of
pixels on target on the iris. For an imaging system that will
attempt to accomplish both of these objectives, the requirements of
the two tasks are largely at odds. Finally, both problems are
further complicated by occlusion by the eyelids and eyelashes.
Embodiments of the imaging systems described herein may address at
least some of these problems.
[0088] FIGS. 10A and 10B schematically illustrate an example of an
imaging system 1000a configured to image one or both eyes 210, 220
of a wearer 90. The imaging system 1000a comprises a substrate 1070
and a camera assembly 1030 arranged to view the eye 220.
Embodiments of the imaging system 1000a described herein with
reference to FIGS. 10A and 10B can be used with HMDs including the
display devices described herein (e.g., the wearable display system
200 shown in FIG. 2, the display system 250 shown in FIGS. 6 and 7,
and the stack 660 of FIGS. 9A-9C). For example, in some
implementations where the imaging system 1000a is part of the
display system 250 of FIG. 6, the substrate 1070 may replace one of
the waveguides 270, 280, 290, 300, or 310, may be disposed between
the of waveguide stack 260 and eye 210, or may be disposed between
the waveguide stack 260 and the world 510.
[0089] In some embodiments, the camera assembly 1030 may be mounted
in proximity to the wearer's eye, for example, on a frame 80 of the
wearable display system 60 of FIG. 2 (e.g., on an ear stem 82 near
the wearer's temple); around the edges of the display 70 of FIG. 2
(as shown in FIG. 10B); or embedded in the display 70 of FIG. 2.
The camera assembly 1030 may be substantially similar to camera
assembly 630 of FIG. 6. In other embodiments, a second camera
assembly can be used for separately imaging the wearer's other eye
210. The camera assembly 1030 can include an IR digital camera that
is sensitive to IR radiation. The camera assembly 1030 can be
mounted so that it is forward facing (e.g., in the direction of the
wearer's vision toward), as illustrated in FIG. 10A, or the camera
assembly 1030 can be mounted to be facing backward and directed at
the eye 220 (e.g., FIG. 10B).
[0090] In some embodiments, the camera assembly 1030 may include an
image capture device and a light source 1032 to project light to
the eye 220, which may then be reflected by the eye 220 and
detected by the camera assembly 1030. While the light source 1032
is illustrated as attached to the camera assembly 1030, the light
source 1032 may be disposed in other areas with respect to the
camera assembly such that light emitted by the light source is
directed to the eye of the wearer and reflected to the camera
assembly 1030. For example, where the imaging system 1000a is part
of the display system 250 (FIG. 6) and the substrate 1070 replaces
one of waveguides 270, 280, 290, 300, or 310, the light source 1032
may be one of light emitters 360, 370, 380, 390, or light source
530.
[0091] In the embodiment illustrated in FIG. 10A, the camera
assembly 1030 is positioned to view a proximal surface 1074 of the
substrate 1070. The substrate 1070 can be, for example, a portion
of the display 70 of FIG. 2 or a lens in a pair of eyeglasses. The
substrate 1070 can be transmissive to at least 10%, 20%, 30%, 40%,
50%, or more of visible light incident on the substrate 1070. In
other embodiments, the substrate 1070 need not be transparent
(e.g., in a virtual reality display). The substrate 1070 can
comprise one or more coupling optical elements 1078. In some
embodiments, the coupling optical elements 1078 may be selected to
reflect a first range of wavelengths while being substantially
transmissive to a second range of wavelengths different from the
first range of wavelengths. In some embodiments, the first range of
wavelengths can be IR wavelengths, and the second range of
wavelengths can be visible wavelengths. The substrate 1070 may
comprise a polymer or plastic material such as polycarbonate or
other lightweight materials having the desired optical properties.
Without subscribing to a particular scientific theory, plastic
materials may be less rigid and thus less susceptible to breakage
or defects during use. Plastic materials may also be lightweight,
thus, when combined with the rigidity of the plastic materials
allowing thinner substrates, may facilitate manufacturing of
compact and light weight imaging systems. While the substrate 1070
is described as comprising a polymer such as polycarbonate or other
plastic having the desired optical properties, other materials are
possible, such as glass having the desired optical properties, for
example, fused silica.
[0092] The coupling optical elements 1078 can comprise a reflective
optical element configured to reflect or redirect light of a first
range of wavelengths (e.g., IR light) while transmitting light of a
second range of wavelengths (e.g., visible light). In such
embodiments, IR light 1010a, 1012a, and 1014a from the eye 220
propagates to and reflects from the coupling optical elements 1078,
resulting in reflected IR light 1010b, 1012b, 1014b which can be
imaged by the camera assembly 1030. In some embodiments, the camera
assembly 1030 can be sensitive to or able to capture at least a
subset (such as a non-empty subset or a subset of less than all) of
the first range of wavelengths reflected by the coupling optical
elements 1078. For example, where the coupling optical elements
1078 is a reflective element, the coupling optical elements 1078
may reflect IR light in the a range of 700 nm to 1.5 .mu.m, and the
camera assembly 1030 may be sensitive to or able to capture near IR
light at wavelengths from 700 nm to 900 nm. As another example, the
coupling optical elements 1078 may reflect IR light in the a range
of 700 nm to 1.5 .mu.m, and the camera assembly 1030 may include a
filter that filters out IR light in the range of 900 nm to 1.5
.mu.m such that the camera assembly 1030 can capture near IR light
at wavelengths from 700 nm to 900 nm.
[0093] Visible light from the outside world (e.g., world 510 of
FIG. 6) can be transmitted through the substrate 1070 and perceived
by the wearer. In effect, the imaging system 1000a can act as if
there were a virtual camera assembly 1030c directed back toward the
wearer's eye 220 capturing a direct view image of the eye 220.
Virtual camera assembly 1030c is labeled with reference to "c"
because it may image virtual IR light 1010c, 1012c, and 1014c
(shown as dotted lines) propagated from the wearer's eye 220
through the substrate 1070. Although coupling optical elements 1078
is illustrated as disposed on the proximal surface 1074 of the
substrate 1070, other configurations are possible. For example, the
coupling optical elements 1078 can be disposed on a distal surface
1076 of the substrate 1060 or within the substrate 1070. In
implementations where the substrate 1070 is part of display system
250 of FIG. 6, the coupling optical element 1078 may be an
out-coupling optical element 570, 580, 590, 600, or 610.
[0094] While an example arrangement of imaging system 1000a is
shown in FIG. 10A, other arrangements are possible. For example,
multiple coupling optical elements may be used and configured to
in-couple light into the substrate 1070 via TIR and out-couple the
light to the camera assembly 1030, for example, as will be
described in connection to FIGS. 11-18. While the coupling optical
elements 1078 have been described as reflective optical elements,
other configurations are possible. For example, the coupling
optical elements 1078 may be a transmissive coupling optical
element that substantially transmits a first and a second range of
wavelengths. The transmissive coupling optical element may refract
a first wavelength at an angle, for example, to induce TIR within
the substrate 1070, while permitting the second range of
wavelengths to pass substantially unhindered.
[0095] Example Imaging Systems for Off-Axis Imaging Using Multiple
Coupling Optical Elements
[0096] FIG. 11 schematically illustrates another example imaging
system 1000b comprising multiple coupling optical elements to
totally internally reflect light from an object through a substrate
1070 to image an object at a camera assembly 1030. FIG. 11
illustrates an embodiment of imaging system 1000b comprising a
substrate 1070 comprising at least two coupling optical elements
1178a, 1188a disposed on one or more surfaces of the substrate 1070
and a camera assembly 1030 arranged to view an object positioned at
an object plane 1120. While a specific arrangement is depicted in
FIG. 11, this is for illustrative purposes only and not intended to
be limiting. Other optical elements (for example, lenses,
waveguides, polarizers, prisms, etc.) may be used to manipulate the
light from the object so to focus, correct aberrations, direct,
etc., the light as desired for the specific application.
[0097] In the embodiment of FIG. 11, the substrate 1070 includes
two coupling optical elements 1178a, 1188a, each disposed adjacent
to the distal and proximal surfaces 1076, 1074 of the substrate
1070, respectively. In some embodiments, the coupling optical
elements 1178a, 1188a may be attached or fixed to the surfaces of
the substrate 1070. In other embodiments, one or more of the
coupling optical element 1178a, 1188a may be embedded in the
substrate 1070 or etched onto the surfaces of the substrate 1070.
Yet, in other embodiments, alone or in combination, the substrate
1070 may be manufactured to have a region comprising the coupling
optical elements 1178a, 1188a as part of the substrate 1070 itself.
While an example arrangement of the coupling optical elements
1178a, 1188a is shown in FIG. 11, other configurations are
possible. For example, coupling optical elements 1178a, 1188a may
both be positioned adjacent to the distal surface 1076 or proximal
surface 1074 (as illustrated in FIGS. 12A, 13A, 13B, and 14B) or
coupling optical elements 1178a may be positioned on the proximal
surface 1074 while coupling optical elements 1188a is positioned on
the distal surface 1076 (as illustrated in FIG. 14A).
[0098] The coupling optical elements 1178a and 1188a may be similar
to the coupling optical elements 1078 of FIGS. 10A and 10B. For
example, FIG. 11 illustrates the imaging system 1000b where both
coupling optical elements 1178a, 1188a are reflective coupling
optical elements that are wavelength selective, such that they
selectively redirect one or more wavelengths of light, while
transmitting other wavelengths of light, as described above in
connection to FIG. 10A. In some embodiments, the coupling optical
elements 1178a and 1188a deflect light of a first wavelength range
(e.g., IR light, near-IR light, etc.) while transmitting a second
wavelength range (e.g., visible light). As described below, the
coupling optical elements 1178a, 1188a may comprise diffractive
features forming a diffraction patter (e.g., a DOE).
[0099] Referring to FIG. 11, the camera assembly 1030 is mounted
backward facing toward the object plane 1120 and viewing the distal
surface 1076. In various embodiments, the camera assembly 1030 may
be mounted in proximity to the wearer's eye (for example on the
frame 80 of FIG. 2) and may include light source 1032 (not shown in
FIG. 11). The camera assembly 1030 can include an IR digital camera
that is sensitive to IR radiation. While the camera assembly 1030
of FIG. 11 is shown as backward facing, other arrangements are
possible. For example, camera assembly 1030 can be mounted so that
it is forward facing.
[0100] In some embodiments, an object (e.g., the eye 220 or a part
thereof) at the object plane 1120 may be illuminated by the light
source 1032 (FIGS. 10A and 10B). For example, where the pupil is to
be imaged, the light source 1032 is directed thereto and
illuminates the pupil of eye 220. In other embodiments, the first
Purkinje image, which is the virtual image formed by the reflection
of a point source off the anterior surface of the cornea may be
imaged. Any physical or optical object associated with the eye that
can be uniquely identified and that will indicate eye position,
pupil position, or gaze direction may be imaged. Upon illumination,
the object may reflect the light toward the substrate 1070 as light
rays 1122a-e (collectively referred to hereinafter as "1122"). For
example, light rays 1122a-e may be illustrative of diffuse light
reflected from the pupil, iris, eyelid, sclera, other tissue around
the eye, etc. In another example, light rays 1122a-e may be
illustrative of specularly reflected light from a glint (e.g., a
Purkinje image). Without subscribing to a scientific theory, a
reflection from the eye, parts of the eye, or tissue around the eye
may rotate the polarization of the incident light depending on the
orientation of the illumination. In some embodiments, the light
source 1032 (FIGS. 10A and 10B) may be a LED light source that does
not have a specific polarization, unless a polarizer is implemented
in the optical path with may reduce the intensity of the light, for
example, by as much of 50%. While only light rays 1122 are shown in
FIG. 11, this is for illustrative purposes only and any number of
reflected light rays are possible. Each of light rays 1122 may be
reflected at the same or different angles from the object. For
example, FIG. 11 illustrates that light ray 1122a is reflected at a
first angle that may be larger than the angle at which light ray
1122e is reflected from the object. Other configurations are
possible.
[0101] While the above description referred to light rays 1122 as
reflected from the object, other configurations are possible. In
some embodiments, the light rays 1122 are emitted by a light source
located at the object plane 1120 instead of reflecting light from
the source 1032 (FIGS. 10A and 10B). As such, the light rays 1122
may be directed toward the substrate 1070. It will be understood
that light rays 1122 may be all or some of the light reflected from
or emitted by the object plane 1120.
[0102] As illustrated in FIG. 11, upon emanating from the object
plane 1120, the light rays 1122 are incident on the proximal
surface 1074 of the substrate at an angle of incidence relative to
an imaginary axis perpendicular to the proximal surface 1074 at the
point of incidence. The light rays 1122 then enter the substrate
1070 and are refracted based, in part, on angle of incidence at the
proximal surface 1074 and the ratio of the refractive indices of
the substrate 1070 and the medium immediately adjacent to the
proximal surface 1074.
[0103] The light rays 1122 travel to and impinge upon the coupling
optical element 1178a at an angle of incidence relative to an
imaginary axis perpendicular to the distal surface 1076 at the
point of incidence. The light rays 1122 are deflected by the
coupling optical element 1178a so that they propagate through the
substrate 1070; that is, the coupling optical element 1178a
functions as a reflective in-coupling optical element that reflects
the light into the substrate 1070. The light rays 1122 are
reflected at angles such that the in-coupled light rays 1122
propagate through the substrate in lateral direction toward the
coupling optical element 1188a by total internal reflection.
Without subscribing to any scientific theory, the total internal
reflection condition can be satisfied when the diffraction angle
.theta. between the incident light and the perpendicular axis is
greater than the critical angle, .theta..sub.C, of the substrate
1070. Under some circumstances, the total internal reflection
condition can be expressed as:
sin(.theta..sub.C)=n.sub.o/n.sub.s [1]
where n.sub.s is the refractive index of the substrate 1070 and
n.sub.o is the refractive index of the medium adjacent to the
surface substrate 1070. According to various embodiments, n.sub.s
may be between about 1 and about 2, between about 1.4 and about
1.8, between about 1.5 and about 1.7, or other suitable range. For
example, the substrate 1070 may comprise a polymer such as
polycarbonate or a glass (e.g., fused silica, etc.). In some
embodiments, the substrate 1070 may be 1 to 2 millimeters thick,
from the proximal surface 1074 to the distal surface 1076. For
example, the substrate 1070 may be a 2 millimeter thick portion of
fused silica or a 1 millimeter thick portion of polycarbonate.
Other configurations are possible to achieve the desired operation
and image quality at the camera assembly 1030.
[0104] In some embodiments, the substrate 1070 may be formed of
high refractive index material (e.g., materials having a higher
refractive index than the medium immediately adjacent to the
substrate 1070). For example, the refractive index of the material
immediately adjacent to the substrate 1070 may be less than the
substrate refractive index by 0.05 or more, or 0.10 or more.
Without subscribing to a particular scientific theory, the lower
refractive index medium may function to facilitate TIR of light
through the substrate 1070 (e.g., TIR between the proximal and
distal surfaces 1074, 1076 of the substrate 1070). In some
embodiments, the immediately adjacent medium comprises air with a
refractive index n.sub.o of about 1. Critical angles can be in a
range from 20 degrees to 50 degrees, depending on the substrate
material and surrounding medium. In other embodiments, alone or in
combination, the immediately adjacent medium may comprise other
structures and layers, for example, one or more of the layers
described in connection to FIGS. 6 and 9A-9C may be immediately
adjacent to either the proximal or distal surface 1074, 1076 of the
substrate 1070.
[0105] The light then propagates through the substrate 1070 in a
direction generally parallel with the surfaces of the substrate
1070 and toward the coupling optical element 1188a. Generally
toward may refer to the condition that the light rays 1122 are
reflected between the surfaces of the substrate 1070 and as such
travel in directions that may not be exactly parallel to the
substrate 1070, but the overall direction of travel is
substantially parallel with the surfaces of the substrate. The
light rays 1122 propagate through the substrate 1070 by TIR until
impinging on the coupling optical element 1188a. Upon reaching the
coupling optical element 1188a, the light rays 1122 are deflected
so that they propagate out of the substrate 1070; that is, the
coupling optical element 1188a functions as a reflective
out-coupling optical element that reflects the light out of the
substrate 1070. The light rays 1120 are reflected at angles such
that the TIR condition is no longer satisfied (e.g., the
diffraction angle .theta. is less than the critical angle
.theta..sub.C). The coupling optical element 1188a may also reflect
the light rays 1122 at an angle toward the camera assembly 1030.
For example, the light rays 1122 may be reflected at an angle so as
to exit the substrate 1070, are refracted by the interface at the
distal surface 1076, and propagate to the camera assembly 1030. The
camera assembly 1030 then receives the light rays 1122 and images
the object plane 1120 based thereon.
[0106] While FIG. 11 illustrates a configuration in which light
travels from coupling optical element 1178a to coupling optical
element 1188a with two instances of total internal reflection,
other configurations are possible. For example, the light rays 1122
may be totally internally reflected any number of times (e.g., 1,
2, 3, 4, 5, 6, 7, etc.) such that the light rays 1122 travel
through the substrate 1070 toward the camera assembly 1030. The
camera assembly 1030 may thus be positioned anywhere and configured
to capture a direct view image at some distance from the object.
Without subscribing to a scientific theory, TIR maybe include
highly efficiency, substantially lossless reflections, thus the
number of times the light rays 1122 TIR may be selected based on
the desired position of the camera. However, in some embodiments,
some leakage, even minimal, may occur at each reflection within the
substrate 1070. Thus, minimizing the number of reflections within
the substrate 1070 may reduce leakage of light and improve image
capture performance. Furthermore, without subscribing to a
scientific theory, reducing the number of reflections may improve
image quality by reducing image blurring or brightness reduction
(e.g., fewer reflections may produce a brighter more intense image)
due to impurity or non-uniform surfaces of the substrate 1070.
Therefore, design of the imaging systems described, and the
components thereof, may be optimized with these considerations in
mind so as to minimize the number of TIR events and position the
camera assembly 1030 as desired.
[0107] Efficient in- and out-coupling of light into the substrate
1070 can be a challenge in designing waveguide-based see-through
displays, e.g., for virtual/augmented/mixed reality display
applications. For these and other applications, it may be desirable
to include diffraction gratings formed of a material whose
structure is configurable to optimize various optical properties,
including diffraction properties. The desirable diffraction
properties may include, among other properties, polarization
selectivity, spectral selectivity, angular selectivity, high
spectral bandwidth, and high diffraction efficiencies, among other
properties. To address these and other needs, in various
embodiments disclosed herein, the coupling optical elements 1178a,
1188a may comprise diffractive features that form a diffraction
pattern, such as DOEs or diffraction gratings.
[0108] Generally, diffraction gratings have a periodic structure,
which splits and diffracts light into several beams traveling in
different directions. The direction of the beams depends, among
other things, on the period of the periodic structure and the
wavelength of the light. The period may be, in part, based on the
grating spatial frequency of the diffractive features. To optimize
certain optical properties, e.g., diffraction efficiencies and
reduce potential rainbow effects, for certain applications such as
in- and out-coupling light from the substrate 1070, various
material properties of the DOE can be optimized for a given
wavelength. For example, where IR light is used, the spatial
frequency of the DOEs 1178a, 1188a may between 600 and 2000 lines
per millimeter. In one embodiment, the spatial frequency may be
approximately 1013 lines per millimeter (e.g., FIGS. 12A and 13A).
In one embodiment, the example DOE 1178a of FIG. 11 may have
1013.95 lines per millimeter. In another embodiment, the spatial
frequency is approximately 1400 lines per millimeter, as described
in connection to FIG. 15. Thus, the spatial frequency of the
coupling optical elements 1178a, 1188a may be, at least, one
consideration when optimizing the imaging systems described herein.
For example, the spatial frequency may be selected to support TIR
conditions. As another example, alone or in combination, the
spatial frequency may be selected to maximize light throughput with
minimum artifacts (e.g., ghost or duplicative images as described
in FIG. 12B) depending on the configuration and dimensions of the
components of the imaging system. In some embodiments, the
diffractive features may have any configurations; however the first
coupling optical element 1178a may be optimized to have minimal or
no visual artifacts (e.g., rainbow effects) because the first
coupling optical element 1178a may be positioned within the user's
field of view.
[0109] In some implementations, the DOE may be an off-axis DOE, an
off-axis Holographic Optical Element (HOE), an off-axis holographic
mirror (OAHM), or an off-axis volumetric diffractive optical
element (OAVDOE). In some embodiments, an OAHM may have optical
power as well, in which case it can be an off-axis volumetric
diffractive optical element (OAVDOE). In some embodiments, one or
more of the coupling optical elements 1178a, 1188a may be an
off-axis cholesteric liquid crystal diffraction grating (OACLCG)
which can be configured to optimize, among other things,
polarization selectivity, bandwidth, phase profile, spatial
variation of diffraction properties, spectral selectivity and high
diffraction efficiencies. For example, any of the CLCs or CLCGs
described in U.S. patent application Ser. No. 15/835,108, filed
Dec. 7, 2017, entitled "Diffractive Devices Based On Cholesteric
Liquid Crystal," which is incorporated by reference herein in its
entirety for all it discloses, can be implemented as coupling
optical elements as described herein. In some embodiments, one or
more coupling optical elements 1178a, 1188a may be switchable DOEs
that can be switched between "on" states in which they actively
diffract, and "off" states in which they do not significantly
diffract.
[0110] In some embodiments, one or more of the coupling optical
elements 1178a, 1188a may be any reflective or transmissive liquid
crystal gratings. The above described CLCs or CLCGs may be one
example of a liquid crystal grating. Other liquid crystal gratings
may also include liquid crystal features and/or patterns that have
a size less than the wavelength of visible light and may comprise
what are referred to as Pancharatnam-Berry Phase Effect (PBPE)
structures, metasurfaces, or metamaterials. For example, any of the
PBPE structures, metasurfaces, or metamaterials described in U.S.
Patent Publication No. 2017/0010466, entitled "Display System With
Optical Elements For In-Coupling Multiplexed Light Streams"; U.S.
patent application Ser. No. 15/879,005, filed Jan. 24, 2018,
entitled "Antireflection Coatings For Metasurfaces"; or U.S. patent
application Ser. No. 15/841,037, filed Dec. 13, 2017, entitled
"Patterning Of Liquid Crystals Using Soft-Imprint Replication Of
Surface Alignment Patterns," each of which is incorporated by
reference herein in its entirety for all it discloses, can be
implemented as coupling optical elements as described herein. Such
structures may be configured for manipulating light, such as for
beam steering, wavefront shaping, separating wavelengths and/or
polarizations, and combining different wavelengths and/or
polarizations can include liquid crystal gratings with metasurface,
otherwise referred to as metamaterials liquid crystal gratings or
liquid crystal gratings with PBPE structures. Liquid crystal
gratings with PBPE structures can combine the high diffraction
efficiency and low sensitivity to angle of incidence of liquid
crystal gratings with the high wavelength sensitivity of the PBPE
structures.
[0111] In some embodiments, certain DOEs may provide non-limiting
advantages when utilized as the coupling optical elements as
described herein. For example, without subscribing to a scientific
theory, liquid crystal gratings, CLCs, CLCGs, volume phase
gratings, and meta-surface gratings may comprise optical properties
configured to reduce or eliminate the appearance of visual
artifacts, such as rainbow effects described above and herein. In
some embodiments, when employing these DOEs, it may be desirable to
illuminate the DOE with polarized light (e.g., the light rays 1122
may include a desired polarization) to maximize the throughput of
light into the substrate 1070. However, as described above, the eye
may rotate the polarization of incident depending on the
orientation, thus, in some embodiments, the light source 1030 may
emit un-polarized light. The reflected light rays 1122 may also be
un-polarized, thus a portion of the light may not be throughput due
to the polarization properties of the DOE (e.g., up to 50% of the
light ray 1122 may be lost at the coupling optical element 1178a).
In some embodiments, to improve throughput, a double layer DOE may
be used as the coupling optical element 1178a. For example, a first
DOE layer configured to operate at one polarization state and as
second DOE layer configured to operate at a second polarization
state.
[0112] For some embodiments, it may be desirable to use DOEs having
sufficiently high diffraction efficiency so that as much of the
light rays 1122 are in-coupled into the substrate 1070 and
out-coupled toward the camera assembly. Without subscribing to a
scientific theory, relatively high diffraction efficiency may
permit directing substantially all of the light received at the
coupling optical element 1178a to the camera assembly 1030, thereby
improving image quality and accuracy. In some embodiments, the
diffraction efficiency may be based, in part, on the sensitivity of
the camera assembly 1030 (e.g., a higher sensitivity may permit a
lower diffraction efficiency). In various embodiments, a DOE may be
selected to have a high diffractive efficiency with respect to a
first range of wavelengths (e.g., IR light) and low diffractive
efficiency in a second range of wavelengths (e.g., visible light).
Without subscribing to a scientific theory, a low diffractive
efficiency with respect to visible light may reduce rainbow effects
in the viewing path of the user.
[0113] In some applications, a DOE may cause a rainbow effect when
a user views visible light through diffractive features. Without
subscribing to a particular scientific theory, the rainbow affect
may be the result of a range of wavelengths interacting with the
diffractive features, thereby deflecting different wavelengths
(e.g., colors) in different directions a different diffraction
angles. In some embodiments described herein, the rainbow effect
from the world interacting with the coupling optical elements
1178a, 1188b as viewed by a user may be reduced by modifying or
controlling the diffractive features to reduce this effect. For
example, since the diffraction angle of light on a DOE is based on
the period or spatial frequency of the grating, the shape of the
diffractive features may be selected to concentrate the majority of
the diffracted light at a particular location for a given range of
wavelengths (e.g., a triangular cross section or blazing).
[0114] In some embodiments, the substrate 1070 may be one of the
waveguides 270, 280, 290, 300, or 310 of FIG. 6. In this
embodiment, the corresponding out-coupling optical element 570,
580, 590, 600, or 610 may be replaced with an in-coupling optical
element 1178a configured to induce TIR of light reflected by the
eye. In some embodiments, a portion of out-coupling optical element
570, 580, 590, 600, or 610 may be replaced with an in-coupling
optical element 1178, such that the corresponding waveguide 270,
280, 290, 300, or 310 may be used as described in connection to
FIG. 6 and to direct light reflected to camera assembly 630.
[0115] In some embodiments, the substrate 1070 may be one the
waveguides 670, 680, or 690 of FIGS. 9A-9C. In these embodiments,
the corresponding light distributing elements 800, 810, and 830, or
a portion thereof, may be replaced with the in-coupling optical
element 1178a, while the in-coupling optical element 700, 710, and
720, or portion thereof, may be replaced with the out-coupling
optical element 1188a. In some embodiments, the OPEs 730, 740, and
750 may remain in the optical path of the light traveling from the
in-coupling optical element 1178a to the out-coupling optical
element 1188a. However, the OPEs 730, 740, and 750 may be
configured to distribute the light to out-coupling optical element
1188a and also decrease the beam spot size as it propagates.
[0116] In various embodiments, the field of view of the camera
assembly 1030 is configured to be sufficient to image the entire
object plane 1120 (e.g., the eye 220 of FIG. 10, a part thereof, or
tissue surrounding the eye) throughout a variety of field
positions. For example, in the example shown in FIG. 11 the size of
the imaged object plane 1120 may be 30 mm (horizontal) by 16 mm
(vertical). In some embodiments, the coupling optical elements
1178a, 1188a are designed to be large enough to at least match the
size of the object to be imaged; that is the coupling optical
elements 1178a, 1188a are configured to receive light from the full
size of the imaged object. For example, the coupling optical
element 1178a receive light originating from the eye 220. The
coupling optical element 1188 may be sized so as to reflect
substantially all of the light rays 1122 that propagate through the
substrate 1070 toward the camera assembly 1030.
[0117] In various embodiments, other optical elements may be
positioned along the path the light rays 1122 travel. For example,
intervening optical elements may be included between the substrate
1070 and the object plane 1120 for directing the light rays 1122
toward the substrate 1070 at the desired angle. Intervening optical
elements may be included between the camera assembly 1030 and the
substrate 1070 directing and focusing the light rays 1122 toward
the camera assembly 1030 so as to place the camera assembly 1030 at
any desired location. In some embodiments, intervening optical
elements may be used to filter the light rays 1122, change
polarization or correct for aberrations. For example, a corrective
optical element may be positioned along the optical path of the
light rays 1122 arranged to and configured to reduce or eliminate
optical aberrations introduced by the optical components of the
imaging system or, where the imaging system is part of the display
system 250 of FIG. 6, other waveguides or optical elements.
[0118] Alternative Embodiments for Off-Axis Imaging Using Multiple
Coupling Optical Elements
[0119] While FIG. 11 shows an example imaging system 1000b
comprising the substrate 1070 having coupling optical elements
1178a, 1188a configured to TIR light from the object plane 1120
through the substrate 1070, other configurations are possible. For
example, FIG. 11 illustrates both coupling optical elements 1178a,
1188a as reflective coupling optical elements; however, one or both
coupling optical elements may be transmissive coupling optical
elements configured to refract a first range of wavelengths at an
angle satisfying the TIR conditions, while transmitting a second
range of wavelengths substantially through the substrate 1070.
FIGS. 12A-18 illustrate some embodiments of substrate 1070,
however, other configurations are possible.
[0120] FIG. 12A schematically illustrates an example imaging system
1000c. The imaging system 1000c uses multiple coupling optical
elements 1178a, and 1188b to TIR the light 1122 from an object
plane 1220 through the substrate 1070. Similar to FIG. 11, FIG. 12A
illustrates the coupling optical element 1178a as a reflective
coupling optical element disposed on the distal surface 1076 of the
substrate 1070 that in-couples the light ray 1122 into the
substrate 1070. However, while coupling optical element 1188b is
substantially similar to coupling optical element 1188a of FIG. 11,
FIG. 12A illustrates a transmissive coupling optical element 1188b
disposed on the distal surface 1076 of the substrate 1070. Thus,
upon propagating through the substrate 1070 via TIR, the light rays
1122 are reflected a third time on the proximal surface 1074 toward
the transmissive coupling optical element 1188b. The transmissive
coupling optical element 1188b refracts the light rays 1122 at an
angle such that the TIR conditions no longer hold and the light
rays 1122 exit the substrate 1070. For example, where the
transmissive coupling optical element 1188b is a DOE, the light is
refracted based on the spatial frequency of the DOE and are
substantially deflected toward the camera assembly 1030.
[0121] FIG. 12A also illustrates a stray light ray 1222 that is
captured by the camera assembly 1030. For example, stray light ray
1222 is reflected by the object 1120, but instead of propagating
through the coupling optical elements 1178a, 1188b, some or all of
the stray light ray 1222 travels directly toward the camera
assembly 1030. Without subscribing to a particular theory, the
stray light ray 1222 is captured by the camera assembly 1030,
thereby producing a direct view image, as described above. Thus,
the camera assembly 1030 may capture a direct view image based on
the light ray 1222 (e.g., including the narrow FOV and defects
described herein) along with the desired image based on the light
rays 1122 that TIR through the substrate. Since the camera assembly
1030 captures light rays that have traveled along different optical
paths, the final image would include various imperfections. One
such imperfection is illustrated in FIG. 12B, but others are
possible.
[0122] FIG. 12B illustrates an example image 1210 of an object 1120
captured using the camera assembly 1030 of FIG. 12A. In the
illustrative image 1210, the camera assembly 1030 has captured an
image 1210 of, for example, a front face of a laser diode used as
an object and illuminated with an IR light source. While a laser
diode is illustrated in this example, other objects may be used to
similar effect, for example an eye 210 of a user. The image 1210
includes a direct view image 1205 of the laser diode produced by
light ray 1222 and set of images 1240 produced by light rays 1122.
The set of images 1240 includes a desired off-axis image (for
illustrative purposes shown as image 1215) and multiple duplicative
images (collectively illustrated as images 1212) from different
perspectives. Such duplicative images 1212, in some embodiments,
may require post-processing to synthesize a single perspective
image of the object if desired. In other embodiments, the imaging
system may be designed to reduce or eliminate the un-wanted
duplicative images 1212 and direct view image 1205 so as to capture
single perspective image 1215.
[0123] For example, FIGS. 13A and B schematically illustrate
another view of the imaging system 1000c. FIGS. 13A and 13B
illustrate example approach to reduce or eliminate the duplicative
images 1212. Without subscribing to a particular scientific theory,
the duplicative images 1212 may be reduced or substantially
eliminated based on varying the thickness of the substrate 1070
(t), the size of the coupling optical elements 1178a (d.sub.1), and
the stride distance (d.sub.2) of the light rays 1122. The stride
distance (d.sub.2) may refer to a distance parallel to the
substrate 1070 that a light ray travels as it reflects within the
substrate; that is, for example, the distance between two adjacent
points of incidence on the distal surface 1076 of the substrate
1070 due to a single instance of total internal reflection. In some
embodiments, the direct view image 1205 may also be reduced or
removed, for example, by including a coating on the proximal or
distal surface 1074, 1076 close to the object 1220 (e.g., an IR
coating configured to block or reduce IR light from the object
1220).
[0124] For example, ghost images can be reduce or eliminated by
reducing the size (d.sub.1) of the coupling optical element 1178a
to the smallest size and varying the physical arrangement of the
components of the imaging system 1000c such that the stride
distance (d.sub.2) is greater than d.sub.1.
[0125] In some embodiments, it may be desirable to control the
stride distance (d.sub.2) to achieve a large stride distance while
minimizing the size of the coupling optical element 1178a. Without
subscribing to a particular scientific theory, a large stride
distance may reduce the intensity of ghost images or permit
placement of the camera assembly 1030 outside of the stray light
rays 1030. Thus, under some circumstances, the stride distance can
be expressed as:
d.sub.2=2*t*tan(.theta.) [2]
where .theta. is the diffraction angle of a light ray 1122 and t is
the thickness of the substrate 1070. Increasing the stride distance
may be done by increasing the thickness (t) of the substrate or
increasing the diffractive angle (.theta.). As described above, the
diffractive angle (.theta.) may be based on the spatial frequency
or period of the diffractive features. For example, the lowest
light ray 1122e has the smallest diffractive angle (.theta.), thus
to increase the stride distance it may be preferable to increase
this diffractive angle. Furthermore, increasing the thickness of
the substrate 1070 may also increase the stride distance. However,
it may be desirable to balance the thickness of the substrate 1070
against producing lightweight and compact imaging systems. In one
embodiment, the substrate 1070 is a 2.5 millimeter thick piece of
polycarbonate (other materials are possible) and the grating
spatial frequency is 720 lines per millimeter. Various embodiments
may include different substrate thicknesses or grating spatial
frequencies.
[0126] FIGS. 14A and 14B schematically illustrate the examples of
imaging systems with multiple coupling optical elements having an
arrangement that is different than the imaging system 1000a of FIG.
11. As described in FIG. 11, the coupling optical elements are
configured as either in- or out-coupling optical elements for
inducing TIR and directing the light rays 1122 through the
substrate 1070 to the camera assembly 1030. FIGS. 14A and 14B
differ in the variation of the type and placement of the coupling
optical elements.
[0127] For example, FIG. 14A depicts the imaging system 1000d that
is substantially similar to the imaging system 1000b of FIG. 11.
However, the imaging system 1000d comprises a transmissive coupling
optical element 1178b disposed on the proximal surface 1074 of the
substrate 1070 and a transmissive coupling optical element 1188b
disposed on the distal surface 1076 of the substrate 1070. The
transmissive coupling optical element 1178b may be configured as an
in-coupling optical element that is transmissive to but diffracts
the light 1122 of FIG. 11 at a diffraction angle to induce TIR at
the distal surface 1046. The light 1122 may then be directed toward
the transmissive coupling optical element 1188b configured as an
out-coupling optical element, as described above in connection to
FIG. 12A.
[0128] In the embodiment of FIG. 14B, the imaging system 1000e is
substantially similar to the imaging system 1000b of FIG. 11.
However, the imaging system 1000e comprises a transmissive coupling
optical element 1178b and a reflective coupling optical element
1188a disposed on the proximal surface 1074 of the substrate 1070.
The transmissive coupling optical element 1178b may be configured
as an in-coupling optical element transmissive to but diffracts the
light 1122 of FIG. 11 at a diffraction angle to induce TIR at the
distal surface 1046. The light 1122 may then be directed toward the
reflective coupling optical element 1188a configured as an
out-coupling optical element, as described above in connection to
FIG. 11.
[0129] FIG. 15 schematically illustrates another example imaging
system 1000f that is substantially similar to imaging system 1000c
of FIGS. 12A-13B. Similar to the above imaging systems, FIG. 15
illustrates the imaging system 1000f comprising the reflective
coupling optical element 1178a and the transmissive coupling
optical element 1188b disposed on the distal surface 1076 of the
substrate 1070. However, the coupling optical elements 1178a and
1188b comprise a spatial frequency of 1411.765 lines per millimeter
and a pitch of 708.33 nanometers and the substrate is a 1
millimeter thick piece of polycarbonate. Accordingly, relative to
the imaging system 1000c of FIGS. 12A-13B, the light 1122 may TIR
multiple times within the substrate 1070 and the camera assembly
may be shifted further away from the coupling optical element
1178a. Other configurations are possible.
[0130] Alternative Embodiments of Imaging Systems for Off-Axis
Imaging
[0131] While FIG. 11 shows an example imaging system 1000b
comprising the substrate 1070 having coupling optical elements
1178a, 1188a configured to TIR light from the object plane 1120
through the substrate 1070, other configurations are possible.
[0132] For example, FIG. 16 illustrates an imaging system 1000g
comprising a substrate 1070 disposed adjacent to an optical
component 1650. In some embodiments, the optical component 1650 may
be the waveguide stack 260 of FIG. 6 or the waveguide stack 660 of
FIGS. 9A-9C. While the substrate 1070 is illustrated as adjacent to
and between the object 1120 and the optical component 1650, other
configurations are possible. For example, the optical component
1650 may be between the substrate 1070 and the object 1120 or the
substrate 1070 may be part of the optical component 1650. The
substrate 1070 may comprise multiple reflective elements 1678 and
1688. As illustrated in FIG. 16, the light 1122 may travel from the
object 1120 toward the substrate 1070 and interact with the
proximal surface 1074. The light 1122 may be refracted and directed
to reflective element 1678, which reflects the light 1122 at an
angle such that the light TIRs on the proximal surface 1074. Thus,
the light 1122 travels toward the reflective element 1688 via TIR.
The light 1122 may be reflected by the reflective element 1688
toward the camera assembly 1030. Accordingly, the camera assembly
1030 may capture an off-axis image of the object 1120, as if the
camera assembly 1030 was directly viewing the object 1120 (e.g.,
virtual camera assembly 1030c). In some embodiments, one or more of
the reflective elements 1678, 1688 may be "hot mirrors" or comprise
reflective coatings that are reflective in the IR while being
transmissive in the visible spectrum.
[0133] In one embodiment of FIG. 16, the substrate 1070 is a 2
millimeter thick piece of polycarbonate and the proximal surface
1074 is positioned 15.7 millimeters to the right of the object
plane 1120 (e.g., z-direction). The object plane 1120 is 12
millimeters vertically (e.g., y-direction). In some embodiments,
the reflective element 1678 is configured to capture a
substantially ful FOV, where the central light ray 1122c propagates
at 25 degrees down (e.g., negative y-direction) from normal. The
camera assembly 1030 may be positioned 15.7 millimeters down from
the origination of the light ray 1122c and 18.79 millimeters to the
right. In this arrangement, the imaging system 1000g captures an
image as if view from the virtual camera 1030c positioned 10.56
millimeters down and 22.65 millimeters to the right.
[0134] FIG. 17 illustrates an imaging system 1000h comprising a
substrate 1770 disposed adjacent to an optical component 1650
(e.g., an optical cover-glass or a prescription glass), and a
reflective surface 1778 disposed adjacent to the substrate 1770. In
some embodiments, the substrate 1770 may be substantially similar
to the substrate 1070 described above. While a specific arrangement
is shown in FIG. 17, other configurations are possible. For
example, the optical component 1650 may be between the substrate
1650 and the object 1120 or the substrate 1770 may be part of the
optical component 1650. As illustrated in FIG. 17, the light 1122
may travel from the object 1120 toward the optical component 1650
and interact therewith. The light 1122 may then be refracted or
pass through the optical component 1650 as it travels toward the
substrate 1770. After passing through the substrate 1770 (refracted
or passed through), the light 1122 is incident upon the reflective
surface 1778. The reflective surface 1778 may have optical
properties configured to reflect and direct the light 1122 toward
the camera assembly 1030. Accordingly, the camera assembly 1030 may
capture an off-axis image of the object 1120, as if the camera
assembly 1030 was directly viewing the object 1120. In one
embodiment of FIG. 17, the imaging system 1000f is configured to
capture an object plane 1120 that is 16 millimeters by 24
millimeters, where the central light ray 1122c propagates at
positive 17 degrees from normal (shown as line 1790).
[0135] In some embodiments the reflective surface 1778 may be a
surface of a decorative or cosmetic lens or optical component. For
example, a decorative lens may be a lens for use as sunglasses to
filter out sunlight. In another embodiment, the decorative lens may
be a color filtering lens for use in goggles. In yet other
embodiments, the decorative lens may have a colored visual
appearance that is viewable by other people who are not wearing the
lens (e.g., a lens that appears blue, red, etc. to other people).
The decorative lens may also include a color layer that is viewed
by people other than the user. The reflective surface 1778 may be a
reflective coating on the inside surface of the decorative lens.
The reflective coating may be reflective in the IR while being
transmissive in the visible spectrum so that the wearer is able to
view the world. As shown in FIG. 17, the reflective surface 1778
may comprise a concave shape configured to direct the light 1122
toward the camera assembly 1030. However, other configurations are
possible.
[0136] FIG. 18 illustrates an imaging system 1000i comprising a
substrate 1770 disposed adjacent to an optical component 1850 and a
prism 1878 disposed adjacent to the substrate 1770. In some
embodiments, the substrate 1770 may be substantially similar to the
substrate 1070 described above. The optical component 1850 may be
substantially similar to optical component 1650, but may also
comprise one or more of the exit pupil expanders 800, 810, 820 of
FIGS. 9A-9C. While a specific arrangement is shown in FIG. 18,
other configurations are possible. For example, the optical
component 1850 may be between the substrate 1770 and the object
1120 or the substrate 1770 may be part of the optical component
1850. As illustrated in FIG. 18, the light 1122 may travel from the
object 1120 toward the optical component 1850 and interact
therewith. The light 1122 may be refracted or passed through as it
travels toward the optical component 1850. After passing through
the optical component 1850 (refracted or passed through), the light
1122 enters prism 1878 and is reflected by surface 1878a toward the
camera assembly 1030. Accordingly, the camera assembly 1030 may
capture an off-axis image of the object 1120, as if the camera
assembly 1030 was directly viewing the object 1120. In some
embodiments, the prism may be an IR prism, "hot mirror," or the
surface 1878a may comprise reflective coatings that are reflective
in the IR while being transmissive in the visible spectrum. In one
embodiment of FIG. 18, the imaging system 1000i comprises a camera
assembly 1030 having a vertical FOV of 35 degrees and a focal
distance of 30.73 millimeters. Such an imaging system 1000i may be
configured to capture an object plane 1120 that is 16 millimeters
by 24 millimeters, where the central light ray 1122c propagates at
negative 25 degrees from normal (shown as line 1790).
[0137] Example Routine for Imaging an Object
[0138] FIG. 19 is a process flow diagram of an illustrative routine
for imaging an object (e.g., an eye of the user) using an off-axis
camera (e.g., camera assembly 630 of FIG. 6 or camera assembly 1030
of FIG. 10A). The routine 1900 describes how a light from an object
can be can be directed to a camera assembly that is positioned away
from or off-axis relative to the object for imaging the object as
though the camera assembly was pointed directly toward the
object.
[0139] At block 1910, an imaging system is provided that is
configured to receive light from the object and direct the light to
a camera assembly. The imaging system may be one or more of the
imaging systems 1000a-i as described above in connection to FIGS.
10A-11, 12A, and 13A-18. For example, the imaging system may
comprise a substrate (e.g., substrate 1070) comprising a first
coupling optical element (e.g., first coupling optical element
1078, 1178a, or 1178b) and a second coupling optical element (e.g.,
second optical element 1188a or 1188b). The first and second
optical elements may be disposed on a distal surface or a proximal
surface of the substrate as described above and throughout this
disclosure. The first and second optical elements may be laterally
offset from each other along the substrate 1070. As described above
and throughout this disclosure, the first coupling optical element
may be configured to deflect light at an angle to TIR the light
between the proximal and distal surfaces. The first optical element
may be configured to deflect light at an angle generally toward the
second coupling optical element. The second coupling optical
element may be configured to receive the light from the first
coupling optical element and deflect the light at an angle out of
the substrate.
[0140] At block 1920, the light is captured with a camera assembly
(e.g., camera assembly 630 of FIG. 6 or camera assembly 1030 of
FIGS. 10A-11, 12A, and 13A-18). The camera assembly may be
orientated toward the second coupling optical element and to
receive the light deflected by the second coupling optical element.
The camera assembly may be an off-axis camera in a forward facing
or backward facing configuration. At block 1930, an off-axis image
of the object may be produced based on the captured light, as
described herein and throughout this disclosure.
[0141] In some embodiments, the routine 1900 may include an
optional step (not shown) of illuminating the object with light
from a light source (e.g., light source 632 of FIG. 6 or light
source 1032 of FIGS. 10A-11, 12A, and 13A-18). In some embodiments,
the light may comprise range of wavelengths including IR light.
[0142] In some embodiments, the off-axis image produced at block
1930 may be processed and analyzed, for example, using
image-processing techniques. The analyzed off-axis image may be
used to perform one or more of: eye tracking; biometric
identification; multiscopic reconstruction of a shape of an eye;
estimating an accommodation state of an eye; or imaging a retina,
iris, other distinguishing pattern of an eye, and evaluate a
physiological state of the user based, in part, on the analyzed
off-axis image, as described above and throughout this
disclosure.
[0143] In various embodiments, the routine 1900 may be performed by
a hardware processor (e.g., the local processing and data module
140 of FIG. 2) configured to execute instructions stored in a
memory. In other embodiments, a remote computing device (in network
communication with the display apparatus) with computer-executable
instructions can cause the display apparatus to perform aspects of
the routine 1900.
[0144] Additional Aspects
[0145] 1. An optical device comprising: a substrate having a
proximal surface and a distal surface; a first coupling optical
element disposed on one of the proximal surface and the distal
surface; and a second coupling optical element disposed on one of
the proximal surface and the distal surface and laterally offset
from the first coupling optical element along a direction parallel
to the proximal surface or the distal surface, wherein the first
coupling optical element is configured to deflect light at an angle
to totally internally reflect (TIR) the light between the proximal
and distal surfaces and toward the second coupling optical element,
the second coupling optical element configured to deflect light at
an angle out of the substrate.
[0146] 2. The optical device of Aspect 1, wherein the substrate is
transparent to visible light.
[0147] 3. The optical device of Aspect 1 or 2, wherein the
substrate comprises a polymer.
[0148] 4. The optical device of any one of Aspects 1-3, wherein the
substrate comprises polycarbonate.
[0149] 5. The optical device of any one of Aspects 1-4, wherein the
first and second coupling optical elements are external to and
fixed to at least one of the proximal and distal surfaces of the
substrate.
[0150] 6. The optical device of any one of Aspects 1-5, wherein the
first and second coupling optical elements comprise a portion of
the substrate.
[0151] 7. The optical device of any one of Aspects 1-6, wherein at
least one of the first and second coupling optical elements
comprise a plurality of diffractive features.
[0152] 8. The optical device of Aspect 7, wherein the plurality of
diffractive features have a relatively high diffraction efficiency
for a range of wavelengths so as to diffract substantially all of
the light of the range of wavelengths.
[0153] 9. The optical device of Aspect 7 or 8, wherein the
plurality of diffractive features diffract light in at least one
direction based in part on a period of the plurality of diffractive
elements, wherein the at least one direction is selected to TIR the
light between the proximal and distal surfaces.
[0154] 10. The optical device of any one of Aspects 1-7, wherein at
least one of the first or second coupling optical elements
comprises at least one of an off-axis diffractive optical element
(DOE), an off-axis diffraction grating, an off-axis diffractive
optical element (DOE), an off-axis holographic mirror (OAHM), or an
off-axis volumetric diffractive optical element (OAVDOE), or an
off-axis cholesteric liquid crystal diffraction grating
(OACLCG).
[0155] 11. The optical device of any one of Aspects 1-7 and 10,
wherein each of the first and second coupling optical elements are
configured to deflect light of a first range of wavelengths while
transmitting light of a second range of wavelengths.
[0156] 12. The optical device of Aspect 11, wherein the first range
of wavelengths comprises light in at least one of the infrared (IR)
or near-IR spectrum and the second range of wavelengths comprises
light in the visible spectrum.
[0157] 13. The optical device of any one of Aspects 1, 7, and 11,
wherein the first and second coupling optical elements selectively
reflect light of a range of wavelengths, wherein the first coupling
optical element is disposed on the distal surface of the substrate
and the second coupling optical element is disposed on the proximal
surface of the substrate.
[0158] 14. The optical device of any one of Aspects 1, 7, 10, and
11, wherein the first and second coupling optical elements
selectively transmit light of a range of wavelengths, wherein the
first coupling optical element is disposed on the proximal surface
of the substrate and the second coupling optical element is
disposed on the distal surface of the substrate.
[0159] 15. The optical device of any one of Aspects 1, 7, 10, and
11, wherein the first coupling optical element selectively reflects
light of a range of wavelengths and the second coupling optical
element selectively transmits light of the range of wavelengths,
wherein the first and second coupling optical elements are disposed
on the distal surface of the substrate.
[0160] 16. The optical device of any one of Aspects 1, 7, 10, and
11, wherein the first coupling optical element selectively
transmits light of a range of wavelengths and the second coupling
optical element selectively reflects light of the range of
wavelengths, wherein the first and second coupling optical elements
are disposed on the proximal surface of the substrate.
[0161] 17. A head mounted display (HMD) configured to be worn on a
head of a user, the HMD comprising: a frame; a pair of optical
elements supported by the frame such that each optical element of
the pair of optical elements is capable of being disposed forward
of an eye of the user; and an imaging system comprising: a camera
assembly mounted to the frame; and an optical device in accordance
to any one of the Aspects 1-16.
[0162] 18. The HMD of Aspect 17, wherein at least one optical
element of the pair of optical elements comprises the
substrate.
[0163] 19. The HMD of Aspect 17 or 18, wherein the substrate is
disposed on a surface of at least one optical element of the pair
of optical elements.
[0164] 20. The HMD of any one of Aspects 17-19, wherein the frame
comprises a pair of ear stems, and the camera assembly is mounted
on one of the pair of ear stems.
[0165] 21. The HMD of any one of Aspects 17-20, wherein the camera
assembly is a forward facing camera assembly configured to image
light received from the second coupling optical element.
[0166] 22. The HMD of any one of Aspects 17-20, wherein the camera
assembly is a backward facing camera assembly disposed in a
direction facing toward the user, the backward facing camera
assembly configured to image light received from the second
coupling optical element.
[0167] 23. The HMD of any one of Aspects 17-22, further comprising
a light source emitting light of a first range of wavelengths
toward at least one of: the eye of the user, a part of the eye, or
a portion of tissue surrounding the eye.
[0168] 24. The HMD of Aspect 23, wherein the light of the first
range of wavelengths is reflected toward the first coupling optical
element by at least one of: the eye of the user, a part of the eye,
or a portion of tissue surrounding the eye.
[0169] 25. The HMD of any one of Aspects 17-23, wherein each of the
pair of optical elements is transparent to visible light.
[0170] 26. The HMD of any one of Aspects 17-23 and 25, wherein each
of the pair of optical elements is configured to display an image
to the user.
[0171] 27. The HMD of any one of Aspects 17-23, 25, and 26, wherein
camera assembly is configured to image at least one of: the eye of
the user, a part of the eye, or a portion of tissue surrounding the
eye based, in part on, light received from the second coupling
optical element.
[0172] 28. The HMD of Aspect 27, wherein the HMD is configured to
track the gaze of the user based on the image of the at least one
of the: eye of the user, the part of the eye, or the portion of
tissue surrounding the eye.
[0173] 29. The HMD of Aspect 27, wherein the image imaged by the
camera assembly is consistent with an image imaged by a camera
placed in front of the eye of the user and directly viewing the at
least one of the: eye of the user, the part of the eye, or the
portion of tissue surrounding the eye.
[0174] 30. The HMD of any one of Aspects 17-23, 25, and 27, wherein
the optical device is arranged to reduce stray light received by
the camera assembly.
[0175] 31. The HMD of any one of Aspects 17-23, 25, 27, and 30,
wherein a size of the first coupling optical element is less than a
stride distance of the light reflected in the between the distal
and proximal surfaces of the substrate, wherein the stride distance
is based on a thickness of the substrate and the angle at which the
first coupling optical element deflects the light.
[0176] 32. The HMD of Aspect 31, wherein the size of the first
coupling optical element is based on the field of view of the eye
of the user.
[0177] 33. The HMD of any one of Aspects 17-23, 25, 27, 30, and 31,
wherein an image of the eye of the user imaged by the camera
assembly and an image of the eye of the user imaged by a camera
placed in front of the eye of the user are indistinguishable.
[0178] 34. The HMD of any one of Aspects 17-23, 25, 27, 30, 31, and
33, further comprising: a non-transitory data storage configured to
store imagery acquired by the camera assembly; and a hardware
processor in communication with the non-transitory data storage,
the hardware processor programmed with executable instructions to
analyze the imagery, and perform one or more of: eye tracking;
biometric identification; multiscopic reconstruction of a shape of
an eye; estimating an accommodation state of an eye; or imaging a
retina, iris, other distinguishing pattern of an eye, and evaluate
a physiological state of the user.
[0179] 35. An imaging system comprising: a substrate having a
proximal surface and a distal surface, the substrate comprising: a
first diffractive optical element disposed on one of the proximal
surface and the distal surface; and a second diffractive optical
element disposed on one of the proximal surface and the distal
surface, the second diffractive optical element offset from the
first diffractive optical element along a direction parallel to the
proximal surface or the distal surface, wherein the first
diffractive optical element is configured to deflect light at an
angle to totally internally reflect (TIR) the light between the
proximal and distal surfaces and toward the second coupling optical
element, the second diffractive optical element configured to
deflect light incident thereon at an angle out of the substrate;
and a camera assembly to image the light deflected by the second
diffractive optical element.
[0180] 36. The imaging system of Aspect 35, wherein the first and
second diffractive optical elements comprise at least one of an
off-axis diffractive optical element (DOE), an off-axis diffraction
grating, an off-axis diffractive optical element (DOE), an off-axis
holographic mirror (OAHM), or an off-axis volumetric diffractive
optical element (OAVDOE), an off-axis cholesteric liquid crystal
diffraction grating (OACLCG), a hot mirror, a prism, or a surface
of a decorative lens.
[0181] 37. A method of imaging an object using a virtual camera,
the method comprises: providing an imaging system in front of an
object to be imaged, wherein the imaging system comprises: a
substrate comprising a first coupling optical element and a second
coupling optical element each disposed on one of a proximal surface
and a distal surface of the substrate and offset from each other,
wherein the first coupling optical element is configured to deflect
light at an angle to totally internally reflect (TIR) the light
between the proximal and distal surfaces and toward the second
coupling optical element, the second coupling optical element
configured to deflect the light at an angle out of the substrate;
and capturing the light with a camera assembly oriented to receive
light deflected by the second coupling optical element; and
producing an off-axis image of the object based on the captured
light.
[0182] 38. The method of Aspect 37, wherein each of the first and
second coupling optical elements deflect light of a first range of
wavelengths while transmitting light in a second range of
wavelengths.
[0183] 39. The method of Aspect 37 or 38, further comprising
illuminating the object with a first range of wavelengths emitted
by a light source.
[0184] 40. The method of any one of Aspects 37-39, further
comprising: analyzing the off-axis image, and performing one or
more of: eye tracking; biometric identification; multiscopic
reconstruction of a shape of an eye; estimating an accommodation
state of an eye; or imaging a retina, iris, other distinguishing
pattern of an eye, and evaluate a physiological state of the user
based, in part, on the analyzed off-axis image.
[0185] 41. An imaging system comprising: a substrate having a
proximal surface and a distal surface; a reflective optical element
adjacent to the distal surface, wherein the reflective optical
element is configured to reflect, at an angle, light that has
passed out of the substrate at the distal surface; and a camera
assembly to image the light reflected by the reflective optical
element.
[0186] 42. The imaging system of Aspect 41, wherein the reflective
optical element comprises a surface of a decorative lens.
[0187] 43. The imaging system of Aspect 41 or Aspect 42, wherein
the reflective optical element comprises a reflective coating on a
surface of a decorative lens.
[0188] 44. The imaging system of any one of Aspects 41-43, wherein
the reflective optical element comprises a reflective prism.
[0189] 45. The imaging system of any one of Aspects 41-44, wherein
the reflective optical element is reflective to infrared light and
transmissive to visible light
[0190] 46. The imaging system of any one of Aspects 41-45, further
comprising a diffractive optical element adjacent to the proximal
surface.
[0191] 47. The imaging system of any one of Aspects 41-46, wherein
the camera assembly is a forward facing camera assembly configured
to image light received from the reflective optical element.
[0192] 48. A head mounted display (HMD) configured to be worn on a
head of a user, the HMD comprising: a frame; a pair of optical
elements supported by the frame such that each optical element of
the pair of optical elements is capable of being disposed forward
of an eye of the user; and an imaging system in accordance with any
one of claims 41-47.
[0193] 49. The HMD of Aspect 48, wherein at least one optical
element of the pair of optical elements comprises the
substrate.
[0194] 50. The HMD of Aspect 48 or 49, wherein the substrate is
disposed on a surface of at least one optical element of the pair
of optical elements.
[0195] 51. The HMD of any one of Aspects 48-50, wherein the frame
comprises a pair of ear stems, and the camera assembly is mounted
on one of the pair of ear stems.
[0196] 52. The HMD of any one of Aspects 48-51, further comprising
a light source emitting light of a first range of wavelengths
toward at least one of: the eye of the user, a part of the eye, or
a portion of tissue surrounding the eye.
[0197] 53. The HMD of Aspect any one of Aspects 48-52, wherein each
of the pair of optical elements is transparent to visible
light.
[0198] 54. The HMD of any one of Aspects 48-53, wherein each of the
pair of optical elements is configured to display an image to the
user.
[0199] 55. The HMD of any one of Aspects 48-54, wherein the camera
assembly is configured to image at least one of: the eye of the
user, a part of the eye, or a portion of tissue surrounding the eye
based, in part on, light received from the second coupling optical
element.
[0200] 56. The HMD of any one of Aspects 48-55, wherein the HMD is
configured to track the gaze of the user based on the image of the
at least one of the: eye of the user, the part of the eye, or the
portion of tissue surrounding the eye.
[0201] 57. The HMD of any one of Aspects 48-56, wherein the image
imaged by the camera assembly is consistent with an image imaged by
a camera placed in front of the eye of the user and directly
viewing the at least one of the: eye of the user, the part of the
eye, or the portion of tissue surrounding the eye.
[0202] 58. The HMD of any one of Aspects 48-57, wherein the optical
device is arranged to reduce stray light received by the camera
assembly.
[0203] 59. The HMD of any one of Aspects 48-58, wherein an image of
the eye of the user imaged by the camera assembly and an image of
the eye of the user imaged by a camera placed in front of the eye
of the user are indistinguishable.
[0204] 60. The HMD of any one of Aspects 48-59, further comprising:
a non-transitory data storage configured to store imagery acquired
by the camera assembly; and a hardware processor in communication
with the non-transitory data storage, the hardware processor
programmed with executable instructions to analyze the imagery, and
perform one or more of: eye tracking; biometric identification;
multiscopic reconstruction of a shape of an eye; estimating an
accommodation state of an eye; or imaging a retina, iris, other
distinguishing pattern of an eye, and evaluate a physiological
state of the user.
ADDITIONAL CONSIDERATIONS
[0205] In the embodiments described above, the optical arrangements
have been described in the context of eye-imaging display systems
and, more particularly, augmented reality display systems. It will
be understood, however, that the principles and advantages of the
optical arrangements can be used for other head-mounted display,
optical systems, apparatus, or methods. In the foregoing, it will
be appreciated that any feature of any one of the embodiments can
be combined and/or substituted with any other feature of any other
one of the embodiments.
[0206] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise," "comprising,"
"include," "including," "have" and "having" and the like are to be
construed in an inclusive sense, as opposed to an exclusive or
exhaustive sense; that is to say, in the sense of "including, but
not limited to." The word "coupled", as generally used herein,
refers to two or more elements that may be either directly
connected, or connected by way of one or more intermediate
elements. Likewise, the word "connected", as generally used herein,
refers to two or more elements that may be either directly
connected, or connected by way of one or more intermediate
elements. Depending on the context, "coupled" or "connected" may
refer to an optical coupling or optical connection such that light
is coupled or connected from one optical element to another optical
element. Additionally, the words "herein," "above," "below,"
"infra," "supra," and words of similar import, when used in this
application, shall refer to this application as a whole and not to
any particular portions of this application. Where the context
permits, words in the above Detailed Description using the singular
or plural number may also include the plural or singular number,
respectively. The word "or" in reference to a list of two or more
items is an inclusive (rather than an exclusive) "or", and "or"
covers all of the following interpretations of the word: any of the
items in the list, all of the items in the list, and any
combination of one or more of the items in the list, and does not
exclude other items being added to the list. In addition, the
articles "a," "an," and "the" as used in this application and the
appended claims are to be construed to mean "one or more" or "at
least one" unless specified otherwise.
[0207] As used herein, a phrase referring to "at least one of" a
list of items refers to any combination of those items, including
single members. As an example, "at least one of: A, B, or C" is
intended to cover: A, B, C, A and B, A and C, B and C, and A, B,
and C. Conjunctive language such as the phrase "at least one of X,
Y and Z," unless specifically stated otherwise, is otherwise
understood with the context as used in general to convey that an
item, term, etc. may be at least one of X, Y or Z. Thus, such
conjunctive language is not generally intended to imply that
certain embodiments require at least one of X, at least one of Y
and at least one of Z to each be present.
[0208] Moreover, conditional language used herein, such as, among
others, "can," "could," "might," "may," "e.g.," "for example,"
"such as" and the like, unless specifically stated otherwise, or
otherwise understood within the context as used, is generally
intended to convey that certain embodiments include, while other
embodiments do not include, certain features, elements and/or
states. Thus, such conditional language is not generally intended
to imply that features, elements and/or states are in any way
required for one or more embodiments or whether these features,
elements and/or states are included or are to be performed in any
particular embodiment.
[0209] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the disclosure. Indeed, the novel
apparatus, methods, and systems described herein may be embodied in
a variety of other forms; furthermore, various omissions,
substitutions and changes in the form of the methods and systems
described herein may be made without departing from the spirit of
the disclosure. For example, while blocks are presented in a given
arrangement, alternative embodiments may perform similar
functionalities with different components and/or circuit
topologies, and some blocks may be deleted, moved, added,
subdivided, combined, and/or modified. Each of these blocks may be
implemented in a variety of different ways. Any suitable
combination of the elements and acts of the various embodiments
described above can be combined to provide further embodiments. The
various features and processes described above may be implemented
independently of one another, or may be combined in various ways.
No element or combinations of elements is necessary or
indispensable for all embodiments. All suitable combinations and
subcombinations of features of this disclosure are intended to fall
within the scope of this disclosure.
* * * * *